Prosthetic joint having at least one superhard articulation surface

ABSTRACT

Prosthetic joints, components for prosthetic joints, superhard bearing and articulation surfaces, diamond bearing and articulation surfaces, substrate surface topographical features, materials for making joints, bearing and articulation surfaces, and methods for manufacturing and finishing the same, and related information are disclosed, including a prosthetic joint having at least one superhard articulation surface.

BACKGROUND OF THE INVENTION

A. Field of the Invention

Various embodiments of the invention relate to superhard surfaces andcomponents of various compositions and shapes, methods for making thosesuperhard surfaces and components, and products, which include thosesuperhard surfaces and components. Such products include biomedicaldevices such as prosthetic joints and other devices. More specifically,some preferred embodiments of the invention relate to diamond andpolycrystalline diamond bearing surfaces and prosthetic joints thatinclude diamond and polycrystalline diamond bearing surfaces. Somepreferred embodiments of the invention utilize a polycrystalline diamondcompact (“PDC”) to provide a very strong, low friction, long-wearing andbiocompatible bearing surface in a prosthetic joint. Any bearingsurface, including bearing surfaces outside the field of prostheticjoints, which experience wear and require strength and durability willbenefit from embodiments of the invention.

B. Description of Related Art

This section will discuss art related to prosthetic joint bearingsurfaces. Artificial joint replacement has become a widely acceptedsuccessful medical practice in the treatment of arthritic or deformedjoints. Hundreds of thousands of joint replacement procedures areperformed every year. Prosthetic hip and knee replacement comprise thevast majority of these procedures, however many other joints are alsotreated as well including, but not limited to, the shoulder, elbow,wrist, ankle, and temparomandibular joints. Additionally, there areother joints, such as the intervertebral disk joint of the spine, whichare not commonly replaced with prosthetic joints, but which might beamenable to such treatment to remedy disease states if sufficientlydurable materials in functional designs were available.

The ideal total artificial joint prosthesis can be characterized interms of flexibility, durability, and compatibility. Flexibility: Anideal total joint prosthesis should restore a normal range of motion,allowing all activities possible with a normal natural joint without anincrease in the relative risk of dislocation. Durability: The mechanicalparts of the articulation should function without wearing out orbreaking, and the implant's fixation to the recipient's skeleton shouldremain rigidly intact for the duration of the recipient's lifetime,without requiring restrictions on the intensity of activities or thedegree of load bearing beyond those applying to a natural joint.Compatibility: The prosthetic materials and wear byproducts should bebiocompatible, and should not elicit toxic, inflammatory, immunologic,or other deleterious reactions in the host recipient. Currentlyavailable devices fall short of fulfilling these criteria in one or moresignificant ways. It is the objective of the current invention toimprove upon the prior technologies in terms of meeting these criteria.

In general, there are two types of artificial joints articulating jointsand flexible hinge joints. Articulating joints include hip, knee,shoulder, ankle and other joints. Flexible hinge joints include silasticand metacarpal-phalangeal joints. In the past, articulating joints haveconsisted typically of a hard surface (metal or ceramic) mated to aplastic surface (ultra high molecular weight polyethylene). Other jointshave been composed of variations of hard on hard articulations (metal onmetal and ceramic on ceramic). Articulating joints may take a myriad ofconfigurations including variations on a ball in socket design, such aswith a hip and shoulder joint, and variations on a hinge design as witha knee, elbow, or metacarpal-phalangeal joint. In every case, theprosthesis is designed to restore to the greatest extent possible, thefunctional range of motion, and mechanical stability of the affectedjoint.

As a detailed example of problems found in the prior art, we will reviewthe hip joint. It includes a convex spherical ball (femoral head) and aconcave socket (acetabular socket) articulation. Hip joint replacementconsists of replacing the damaged articular surfaces with newarticulating bearing surfaces. On the acetabluar side, a hemisphere-likecup is placed in the patient's damaged or worn socket, and fixed by somemeans to the patient's bone. On the femoral side, the prostheticreplacement consists of a sphere-like ball designed to fit into, andarticulate with the prosthetic acetabular cup. The sphere-like ball maybe a resurfacing device designed to fit over the patient's own femoralhead (so called “surface replacement”). Or more commonly it consists ofa ball attached to a stem, which is inserted into the femoral canalanchoring the prosthesis to the patient's femur. The ball and socketwork as a pair in similar fashion to the original hip, restoring apartial range of linear and rotational motion.

Alternatively, only a surface replacement or a ball and stem set areprovided without a corresponding socket for a hemiarthroplasty procedure(discussed below). For total hip joint replacement, the most commonlyused device consists of a metal head articulation with a high densityultra high molecular weight polyethylene (UHMWPE) surface, but ceramic(alumina, and partially stabilized zirconia) heads are also used, havingcertain advantages as well as disadvantages relative to their metalcounterparts. Metal on metal, and ceramic on ceramic articulations arealso used in routine medical practice elsewhere in the world, and arebeing used on an investigational basis in the United States.

Replacement of only one half of the hip joint is calledhemiarthroplasty. This is performed when only one of the articulatingportions of the joint is damaged, as with avascular necrosis of thefemoral head, or in the case of a hip fracture that is not amenable torepair. The damaged portion is replaced with a prosthetic articulationdesigned to function with the remaining natural biological portion ofthe joint. The requirements are somewhat different here than with atotal articular replacement, in that the artificial portion must matchthe contours of the anatomic segment, and must be conducive topreservation of the function of the natural segment. This would includehaving a surface smooth enough to minimize wear and tear to the naturaljoint surface, and optimization of surface material properties andcontours that would encourage entrainment of joint fluid into the jointspace. This entrainment of synovial fluid is essential to minimize wearto, and maintain nutrition and function of the biological joint surface.

Prosthetic joint implants must be securely anchored to the recipient'sbone to function properly. This fixation may be achieved through the useof cementing agents, typically consisting of polymethylmethacrylatecement, through biological fixation techniques including directosseointegration to metal or ceramic fixation surfaces and bone ingrowthinto porous surfaces on implant surfaces, or through a mechanicalinterference press fit between the implant and the host bone.Preservation and maintenance of this secure fixation is critical to thelong-term success of the prosthetic construct.

When evaluating prior art technology relative to the criteria previouslyestablished for an ideal prosthetic joint, we find that metal ballsarticulating with polyethylene cups do not provide optimal results. Dueto geometric restrictions on the implant design imposed by implantmaterial properties, and anatomic constraints, artificial hips have adecreased safe range of motion compared to normal natural counterparts.The polyethylene bearings may wear through after between 5 and 20 yearsof service, depending upon factors such as patient age, weight andactivity level. The particulate debris resulting from this normal wearoften results in inflammatory reactions in the bone surrounding andanchoring the implants, resulting in severe erosion of the bone. This iscalled “osteolysis” and has proven to be a most prevalent cause offailure and subsequent artificial joint replacement.

The normal metal to ultra high molecular weight polyethylene (“UHMWPE”)articulation of artificial joints results in the generation of billionsof submicron polyethylene wear particles. It is the accumulation of thiswear-related debris and the immune system's reaction to it that resultsin the inflammatory response, which causes osteolysys. It is also thecumulative effect of this continual wear of UHMWPE that results in wearthrough of the mechanical joint and bearing failure. The younger andmore active the patient, the shorter the anticipated functional life ofthe implant. Thus, those patients who, because of their youth, need thegreatest durability from their implants, typically have the leastdurability.

Osteolysis can cause loosening of the critical implant-bone fixation,and may result in increased risk of fracture of the bone around theimplants. Wear through of the components and/or periprostheticosteolysis of the host bone with associated implant loosening and/orperiprosthetic bone fracture requires major surgical intervention toremove the failed implants, reconstruct the damaged bone, and replacethe failed prosthesis with a new artificial joint. This revision surgeryis typically much more complicated than the initial implant surgery, andcarries with it increased risks for perioperative complications, as wellas increased risks for implant failure as compared to primary artificialjoint replacement. Subsequent failures require further complex surgicalintervention, with continually increasing risks of perioperativecomplications and early implant failure with each episode.

In order to reduce the risks of dislocation, recipients of artificialhips must restrict their range of motion in normal activities,compromising their ability to engage in many routine activities possiblewith normal natural joints. In order to decrease the rate of bearingwear which leads to implant failure due to bearing wear through and/orproblems resulting from debris related osteolysis, they must alsorestrict their activities in terms of intensity, and duration relativeto that routinely possible with normal natural joints.

In an effort to reduce the risk of dislocation, larger diameter bearingshave been tried where the recipient's anatomy permits use of largercomponents. Surface replacement lies at the limit of this approach, andemploys large bearings covering the patient's own femoral head remnant,articulating with a relatively thin UHMWPE acetabular component. Use oflarger diameter bearings results in some increase in safe range ofmotion of the joint. Unfortunately, in the metal/UHMWPE bearing couple,increasing bearing diameter leads to increased rates of debrisgeneration together with increased risk of its associated problems. Inthe case of surface replacements, the thin UHMWPE is particularlysusceptible to accelerated wear, osteolysis, and failure.

The prior art includes many proposed improvements over the typical metalball and polyethylene cup articulation seeking to decrease theseproblems of limited motion, wear, and debris-related osteolysis.

Ceramic bearings have some advantages over prior art metals in aprosthetic joint system. Ceramic bearings have an increased wettabilitycompared to metal, resulting in better boundary layer lubrication, andthey are resistant to the wear-promoting scratches that can develop inmetal heads in the course of normal wear and tear in the joint. Both ofthese factors have contributed to the lower rates of wear and debrisgeneration observed with ceramic on UHMWPE seen in both laboratory andclinical studies.

Unfortunately, ceramic bearings are structurally brittle. This limitsthe number of sizes and neck lengths that can be safely employed inreconstruction, restricting the options available to the surgeon tocomplete an optimal mechanical reconstruction during surgery. Thisintrinsic material brittleness can also lead to sudden implant fractureunder impact, resulting in sudden and often catastrophic implantfailure. Ceramic bearings also suffer from geometric design constraintssimilar to their metal-polyethylene counterparts, and have a similarsusceptibility to dislocation if restrictions on range of motion areviolated by the recipient. The limitations in ceramic materialproperties do not permit the fabrication of surface replacementbearings.

More recently, attention has turned to UHMWPE in an effort to improvethe longevity of these bearing couples. Most early efforts to alterfabrication techniques, such as hot pressed components in hip and kneesystems, and efforts to modify material structure, such as the additionof carbon fibers and the use of a hipping process to increasecrystalinity, have resulted in no demonstrable improvements in clinicalor in vitro performance, and in fact, have often resulted in poorer wearcharacteristics. Other techniques have improved function to a limitedmeasurable extent, such as injection molding of components.

It has been found that the most common sterilization technique used toprepare UHMWPE components for implantation has had extreme unanticipatedeffects upon the material properties and wear characteristics of thismaterial, resulting in accelerated wear and early failure in many cases.Study of this phenomenon, which includes the generation of chemicalcross-links in polyethylene chains, and the generation of persistentfree radicals within the polymer has led to further inventions toeliminate the deleterious effects of this process, while possibly takingadvantage of potential beneficial effects that may actually improve thewear characteristics of polyethylene. These most recent developments,while demonstrating promising results in laboratory simulation studies,have yet to demonstrate improved function in widespread, long-termclinical studies. If these new polyethylene technologies do result indemonstrable improvements in function, the intrinsic problems of metaland ceramic counter bearings may still adversely affect long-termdurability. Ultimate strength of UHMWPE (organic polyethylene bonds) intension, compression and shear are low in comparison with metals,ceramics and diamond bonds. Diamond resistance to wear exceeds that ofall other materials. The table below compares properties ofpolycrystalline diamond compact with some other materials from whichbearing surfaces could be made.

TABLE 1 COMPARISON OF DIAMOND TO OTHER MATERIALS Thermal SpecificHardness Conductivity CTE Material Gravity (Knoop) (W/mK) (× 10⁻⁶)Polycrystalline 3.5-4.0 9000 900 1.50-4.8  Diamond Compact Cubic Boron3.48 4500 800 1.0-4.0 Nitride Silicon Carbide 3.00 2500  84 4.7-5.3Aluminum Oxide 3.50 2000 7.8-8.8 Tungsten Carbide 14.6  2200 112 4-6(10% Co) Cobalt Chrome 8.2  43 RC 16.9 Ti6Al4V 4.43 6.6-17.5 11  Silicon Nitride 3.2  14.2 15-7  1.8-3.7

In order to avoid the potential problems of polyethylene entirely,others have turned to ceramic on ceramic and metal on metal contactsurfaces. Ceramic on ceramic articulations have demonstrated improvedwear rates, and excellent biocompatibility. However they suffer from theintrinsic limitation in material properties seen with ceramic heads usedwith polyethylene- brittleness and fracture risk. In addition, there isa tendency to develop catastrophic accelerated wear when a third bodywear particle of sufficient hardness (such as another fragment ofceramic) is introduced into the articulation. Finally, the materialproperty limitations of ceramic impose minimum material dimensionalthicknesses that preclude the use of larger bearings or application as asurface replacement that would result in gains in effective range ofmotion.

Metal on metal bearings have also demonstrated improved volumetric ratesof wear. And their material properties do make them suitable forapplication in large bearing applications and surface replacementseffectively addressing the need for increased safe range of motion, anddecreased risk of dislocation. However, concern still exists over thecharacter of the wear debris of this metal-metal bearing couple. Thoughvolumetric wear is quite low compared to polyethylene, particle size isextremely minute, on the order of 40-100 angstroms, resulting in an evenlarger total number of particles that with UHMWPE. These wear particlesconsist of cobalt-chrome-molybdenum alloy, which, with theirextraordinarily large combined surface area, can result in significantrelease of metals ions with documented toxicity, and potential for longterm carcinogenicity. It remains for long-term clinical studies todocument the actual risk of this exposure, but significant questionshave been raised with regard to this issue. As with ceramic on ceramicarticulations, metal-to-metal bearings are susceptible to acceleratedwear from third body wear particles.

Thus, the failures and pervasive defects of the prior art show a clearneed for improved prosthetic joints. The various embodiments of theinvention address the many deficiencies left by the prior art byproviding prosthetic joints which are very long lasting, strong, have alow coefficient of friction, are biocompatible, experience little or nowear, and do not shed significant amounts of particles during use.

III. SUMMARY OF THE INVENTION

It is an object of some embodiments of the invention to providecomponents for prosthetic joint implants having increased wearresistance and a decreased coefficient of friction, therefore havingmaximum life of the replaced joint. It is a feature of some embodimentsof the invention that diamond of various types and other superhardmaterials are used for the bearing surfaces of the joint, the superhardmaterials including diamond being very resistant to wear and having avery low coefficient of friction. For the purposes of this document, asuperhard material is a material that has a Knoop hardness of at leastabout 4000. This includes diamond (whether natural diamond or syntheticdiamond), cubic boron nitride and wurzitic boron nitride. It is aconsequent advantage that the joint will likely not wear out during thelifetime of the user and will only generate insignificant amounts ofbenign wear particles.

It is an object of some embodiments of the invention to provide aprosthetic joint that does not shed significant amounts of debris orwear particles as a result of use or wear. It is a feature of someembodiments of the invention that polycrystalline diamond compacts orother superhard materials form at least one of the articulation surfacesof the joint, resulting in a low friction and long wearing joint thatsheds little to no debris or particles during use. Therefore a lessenedrisk of osteolysis is a significant advantage of these embodiments ofthe invention.

It is another object of some preferred embodiments the invention to usethe hardest materials known to man, namely diamond, cubic boron nitrideand other superhard materials to give prosthetic joints the highestresistance to wear currently known to man. It is a feature of theinvention that some preferred embodiments use polycrystalline diamondcompact (“PDC”) for a bearing surface. For the purposes of thisdocument, a polycrystalline diamond compact includes a volume ofsynthetic diamond attached to a substrate material. The polycrystallinediamond is extremely hard and, when polished, has one of the lowestCoefficients of friction of any known material. It is a consequentadvantage of the invention that the joint life far exceeds that of therecipient. The polycrystalline diamond compact may be manufactured by avariety of methods, including high pressure and high temperaturesintering in a press, chemical vapor deposition, physical vapordeposition, and others.

It is another object of some embodiments of the invention to providejoint components, which are completely biocompatible. The most preferredmaterial used in some embodiments of the invention, polycrystallinediamond compact, is extremely biocompatible and elicits minimal ornegligible immune response or other attack by the body. It is anadvantage that the joint will be substantially less disruptive to thebody's systems than prior art joints.

It is another object of some embodiments of the invention to provideimproved geometry within the joint space in order to allow optimalutilization of superhard materials, including polycrystalline diamondcompacts. The improved geometry is intended to limit stresses bothresidual and those imposed during service use. Due to the very hard andstrong nature of the materials being utilized, the entire joint geometrycan be optimized for a particular prosthetic application, rather thansimply copying existing prosthetic joints with new materials.

It is another object of some embodiments of the invention to provide anartificial joint with an improved ball and cup configuration. Theinvented prosthetic hip joint is made from very few components in asimple design, thus contributing to the ease of manufacturability andreliability. The ball and cup are designed to maximize articulationwithin the normal range of movement for a human joint while providingexceptional wear resistance and useful life.

It is another object of some embodiments of the invention to provide acup and ball type prosthetic joint that can be used without a separateshell. Some embodiments of the invention provide an acetabular cup thatmay be fixed to a patient's bone without the need for a separate shell.

It is another object of some embodiments of the invention to provide aprosthetic joint, which combines the use of a polycrystalline diamondcompact bearing surface with a counter-bearing surface of anothermaterial. In some embodiments of the invention, the counter-bearingsurface may be any of a wide variety of materials, including prior artUHMWPE, or even the patient's natural cartilage in the case of ahemiarthroplasty. procedure.

It is another object of some embodiments of the invention to provide amodular prosthetic joint assembly with a superhard bearing surface. Someembodiments of the invention provide modular prosthetic joint componentswhich can be selected and assembled at the time of surgery to provide aprosthetic joint system with dimensions and angular orientation closelyapproximating those of the patient's natural joint. An appropriatesuperhard bearing surface may be provided, such as a polycrystallinediamond compact.

Its is another object of some embodiments of the invention to provide aprosthetic bearing surface useful in hemiarthroplasty procedures. Thenature of the preferred prosthetic joint articulation surface bearingmaterial, polycrystalline diamond, is such that it can be used as abearing material that can articulate against natural cartilage,permitting hemiarthroplasty.

It is another object of some embodiments of the invention to provide areplacement liner or cover for a natural joint. In some embodiments ofthe invention, a femoral head or other natural joint surface may beresurfaced or relined with the invention in order to achieve boneconservation.

It is another object of some embodiments of the invention to providepolycrystalline diamond compacts useful as bearing surfaces withimproved fastening strength between the diamond table and the substrateof the polycrystalline diamond compact. In various embodiments of theinvention, topographical features are provided on the substrate in orderto achieve this improved fastening strength.

It is an object of some embodiments of the invention to providesubstrate configuration that permit the manufacture of spherical,partially spherical and arcuate polycrystalline diamond compacts.Various substrate configurations are disclosed which achieve thisobject.

It is an object of some embodiments of the invention to providenon-planar polycrystalline diamond compact bearing surfaces. Variousembodiments of the invention provide novel bearing surfaces that arenon-planar and preferably are manufactured as polycrystalline diamondcompacts.

It is an object of some embodiments of the invention to provide a methodfor manufacturing non-planar polycrystalline diamond compact bearingsurfaces. Various methods are disclosed for materials preparation andpolycrystalline diamond compact manufacturing that will producenon-planar polycrystalline diamond compact bearing surfaces, includingbut not limited to concave and convex spherical bearing surfaces.

It is an object of some embodiments of the invention to provide methodsfor rough shaping of non-planar polycrystalline diamond compact bearingsurfaces. Novel machining techniques are disclosed which accomplish suchshaping.

It is an object of some embodiments of the invention to provide methodsfor finish polishing of non-planar polycrystalline diamond compactbearing surfaces. Novel polishing techniques are disclosed which permitpolishing of polycrystalline diamond compact bearing surface to behighly polished to a low coefficient of friction.

It is another object of some embodiments of the invention to provide ajoint with enhanced wettability. Use of a diamond bearing surfaceachieves this object.

The objects, features and advantages of the inventions mentioned aboveare exemplary and illustrative only so that the reader may begin toperceive advantages to be accrued by use of the invention alone or incombination with other technology. Additional objects, features andadvantages of the invention will become apparent to persons of ordinaryskill in the art upon reading the specification and claims and viewingthe drawings.

IV. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a side cross-sectional view of a prior art prosthetic hipjoint such as those commonly mounted in the hip of a human.

FIG. 2A depicts an enlarged side cross-sectional view of one embodimentof a prosthetic hip joint made in accordance with the principles of thepresent invention.

FIGS. 2B-G depict various embodiments of prosthetic hip joints of theinvention.

FIGS. 2H-2J depict various acetabular cups of the invention.

FIG. 2K depicts a total prosthetic hip joint of the invention.

FIGS. 2L-2N depict femoral components of prosthetic hip joints of theinvention.

FIGS. 20, 2S, 2T and 2U depict the use of offsets to achieve adjustablegeometry of prosthetic hip joints of the invention.

FIG. 2P depicts a prosthetic femoral head assembly of the invention inuse in a hemiarthroplasty procedure.

FIG. 2Q depicts a prosthetic hip joint of the invention where thefemoral component is a liner used to resurface a natural femoral head.

FIG. 2R depicts a hemiarthorplasty procedure in which the femoralcomponent is a liner used to resurface a natural femoral head.

FIG. 2V depicts a shoulder joint of the invention.

FIG. 2W depicts an elbow joint of the invention.

FIG. 2X depicts a prosthetic wrist joint of the invention.

FIG. 2Y depicts a thrombomandibular joint of the invention.

FIG. 2Z depicts an intervertrebal disc prosthesis of the invention.

FIG. 2AA depicts a thumb or finger prosthesis of the invention.

FIGS. 2AB and 2AC depict a total prosthetic knee joint of the invention.

FIGS. 2AD and 2AE depict a unicompartmental prosthetic knee joint of theinvention.

FIGS. 2AF and 2AG depict a sliding bearing rotating platform prostheticknee joint of the invention.

FIGS. 3A-3U depict substrate surface topographical features desirable insome embodiments of the invention.

FIG. 4A depicts a quantity of diamond feedstock adjacent to a metalalloy substrate prior to sintering of the diamond feedstock and thesubstrate to create a polycrystalline diamond compact.

FIG. 4B depicts a sintered polycrystalline diamond compact in which thediamond table, the substrate, and the transition zone between thediamond table and the substrate are shown.

FIG. 4BB depicts a sintered polycrystalline diamond compact in whichthere is a continuous gradient transition from substrate metal throughthe diamond table.

FIG. 4C depicts a substrate prior to use of a CVD or PVD process forform a volume of diamond on the substrate.

FIG. 4D depicts a diamond compact formed by a CVD or PVD process.

FIGS. 5A and 5B depict two-layer substrates useful for making sphericalor partially spherical polycrystalline diamond compacts.

FIGS. 5C-5G depict alternative substrate configurations for makingspherical or partially spherical polycrystalline diamond compacts withcontinuous and segmented bearing surfaces.

FIGS. 6A depicts an assembly useful for making a convex sphericalpolycrystalline diamond compact.

FIGS. 6B and 6C depict a substrate useful for making concave sphericalpolycrystalline diamond compacts.

FIG. 7 depicts a device, which may be used for loading diamond feedstockprior to sintering.

FIG. 7A depicts a furnace cycle for removal of a binder material fromdiamond feedstock prior to sintering.

FIGS. 8 and 8A depict a precompaction assembly, which may be used toreduce free space in diamond feedstock prior to sintering.

FIG. 8B depicts the anvil arrangement of a high pressure/hightemperature press cubic press and a pressure cube on which it wouldexert pressure in order to sinter diamond.

FIG. 9 depicts EDM roughing of a convex spherical part.

FIG. 10 depicts EDM roughing of a concave spherical part.

FIG. 11 depicts grinding and polishing of a convex spherical part.

FIG. 12 depicts grinding and polishing of a concave spherical part.

V. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made to the drawings in which the various elementsof the present invention will be discussed using a prosthetic hip jointas an example. It will be appreciated that the structures and principlesof the invention can be applied not only to biomedical articulationsurfaces, but also to other types of articulation surfaces, to themanufacture, shaping and finishing of superhard materials and superhardcomponents, and to the manufacture, shaping and finishing of devicesusing superhard articulation surfaces and superhard components. Personsskilled in the design of prosthetic joints and other bearing surfaceswill understand the application of the various embodiments of theinvention and their principles to joints, bearing surfaces and devicesother than those exemplified herein.

A. An Example of the Prior Art

Referring to FIG. 1, a prior art prosthetic hip joint 101 is shown afterinstallation in a patient. The prosthetic hip joint 101 includes a metalor ceramic ball 102, which is connected by a neck 103 to a body 104 anda stem 105. The stem 105 may be held in place in the femur 108 by avariety of methods, including use of cementing agents, an interferencepress fit, a threaded mechanism, and biological fixation.

A cup-shaped socket 106 is anchored in the pelvis 107 by any of avariety of known techniques, such as cementing, press fitting, use ofscrews, use of a textured, knurled or threaded exterior, use of abiological fixation mechanism, or by a combination of biological andmechanical fixation. The ball 102 is positioned so that its sphericalconvex load bearing surface 110 is adjacent the concave load-bearingsurface 112 of the socket 106 so as to permit joint rotation, simulatingthe movement of a natural hip joint. As shown in FIG. 1, a highmolecular weight polymer 111 a is disposed within the socket 106 so asto decrease the friction between the ball 102 and the socket 106,thereby increasing the life of the joint 101. The outer surface of theball 102 is generally referred to as the load-bearing area or surface ofthe ball, as this area interfaces with the load-bearing surface 112 ofthe socket 106 and allows the joint to articulate and rotate.

The disadvantages of such a prosthetic joint are described in detailabove.

B. The Invented Bearing Articulation Surfaces and Related Structures

FIG. 2A illustrates one embodiment of the present invention. FIG. 2Ashows a prosthetic joint 201 and its various constituent components. Thejoint 201 shown includes a ball 202 or femoral head, a neck 203, afragmented view of the body 204 a nd stem 204 a and a socket 205 oracetabular cup. The stem 204 is placed in a receptacle formed in thefemur 108 and is preferably attached to the femur 108 by use of cement232 or another appropriate fixation system. A locking ring such as thatdepicted in FIG. 21 may be used to retain the ball within the socket.

In accordance with the principles of the present invention, the socket205 and/or the ball 202 may be made of durable metal. A list ofappropriate materials is disclosed below. The preferred ball and socketcombination, as depicted, includes a truncated ball 202 that is apolycrystalline diamond compact. The polycrystalline diamond compact hasa quantity or table of polycrystalline diamond 207 sintered to asubstrate material 230. The socket 205 similarly is a polycrystallinediamond compact, having a substrate material 231 on which is sintered atable of polycrystalline diamond 206. In this combination, the bearingor articulation surface 209 of the ball and the bearing or articulationsurface 208 of the socket are spherical in shape and can move, roll andslide with respect to each other in all three dimensions within theconfines of the cup surface. It is preferred that the cup have ahemispherical load bearing and articulation surface (about 180°) formaximum support, strength and mobility in the prosthetic joint.

As discussed in greater detail below, cup and ball will preferably usepolycrystalline diamond compacts in order to form articulation surfaces.In a polycrystalline diamond compact, the diamond tables 206 and 207 arechemically bonded and mechanically fixed to their respective substrates230 and 231 in a manufacturing process that preferably uses acombination of high pressure and high temperature to form the sinteredpolycrystalline diamond (see, e.g., FIGS. 4A-D and related text). Thechemical bonds between the diamond table and the substrate areestablished during the sintering process by combinations of unsatisfiedsp3 carbon bonds with unsatisfied substrate metal bonds. The mechanicalfixation is a result of shape of the substrate and diamond table anddifferences in the physical properties of the substrate and the diamondtable as well as the gradient interface between the substrate and thediamond table. The resulting sintered polycrystalline diamond compactforms a prosthetic joint that is extremely hard, low fiction, durable,impact-resistant, biocompatible and long lasting.

The diamond tables 206 and 207 are preferably polished to a very smoothand glass-like finish to achieve a very low coefficient of friction. Asthe diamond is very hard and the coefficient of friction is very low,the wear between the diamond contact surfaces is almost negligible,resulting in a very long lasting joint. Also due to the hardness,fracture toughness and low coefficient of friction that can be achievedwith polished polycrystalline diamond compacts, the joint is able towithstand substantial impact shock without damage. Polycrystallinediamond also provides the advantage of high surface energy so that it isvery wettable and lubricates well for low wear rates and long life.

While FIG. 2A depicts a prosthetic hip joint that uses both apolycrystalline diamond compact femoral head and a polycrystallinediamond compact acetabular cup, it is possible to use the inventedstructures disclosed herein in other configurations. In some joints, anyof the following materials could be considered for forming a bearingsurface: polycrystalline diamond, monocrystal diamond, natural diamond,diamond created by physical vapor deposition, diamond created bychemical vapor deposition, diamond like carbon, carbonado, cubic boronnitride, hexagonal boron nitride, or a combination of these, polymerssuch as ultra high molecular weight polyethylene (UHMWPE), cross-linkedUHMWPE, poly ether ether ketone, polymer composites, polyurethane,cobalt, chromium, titanium, vanadium, stainless steel, niobium,aluminum, nickel, hafnium, silicon, tungsten, molybdenum, aluminum,zirconium, nitinol, cobalt chrome, cobalt chrome molybdenum, cobaltchrome tungsten, tungsten carbide, titanium carbide, tantalum carbide,zirconium carbide, hafnium carbide, Ti6/4, silicon carbide, chromecarbide, vanadium carbide, yttria stabilized zirconia, magnesiastabilized zirconia, zirconia toughened alumina, titanium molybdenumhafnium, alloys including one or more of the above metals, ceramics,quartz, garnet, sapphire, combinations of these materials, combinationsof these and other materials, and other materials may also be used for abearing surface.

The present preferred material for manufacturing both the ball and cupwear surfaces, however, is a sintered polycrystalline diamond compactdue to its superior performance. Diamond has the greatest hardness andthe lowest coefficient of friction of any currently known material. Thepreferred sintered polycrystalline diamond compacts are chemically andbiologically inert, are impervious to all solvents, and have the highestthermal conductivity at room temperature of any known material. It isalso possible, however, to make an articulating joint in which eitherone or both bearing surfaces are made from materials selected from thetable above, but neither bearing material is diamond.

FIG. 2B depicts a prosthetic hip joint of similar configuration to thatdepicted in FIG. 2 with some important differences. The femoral head 202is a polycrystalline diamond compact that has a diamond table 207 and asubstrate 230 to which it is affixed both mechanically and by chemicalbonds. The cup 205, however, is depicted as an appropriate counterbearing material without a diamond table. The material for the cup 205could be any of those mentioned above as appropriate counter bearingmaterial, a superhard material, a corrosion-resistant metal, ceramic ora polymer material. The load-bearing surface 208, however, must bebiocompatible, durable and have a low coefficient of friction.

FIG. 2C depicts an alternative embodiment of the invention in which thecup 205 is a polycrystalline diamond compact as described above. Theball 202, however, is not a polycrystalline diamond compact and does notinclude a diamond table. The ball 202 could be of any counter bearingmaterial previously referred to, but should have a bearing surface 209that is durable, is biocompatible for prosthetic applications, and has alow coefficient of friction.

FIG. 2D depicts an alternative embodiment of the invention in which theball 202 is an appropriate counter bearing material other than diamond,and the cup 205 is of solid polycrystalline diamond without a substrate.This provides the appropriate load-bearing surface 208 but avoidsconcerns about the body's acceptance of or reaction with a substratematerial in the cup.

FIG. 2E depicts an alternative embodiment of the invention in which thecup 205 may be of any appropriate counter bearing material, such asthose mentioned previously, and the ball 202 is solid polycrystallinediamond.

FIG. 2F depicts an alternative embodiment of the invention in which boththe ball 202 and the cup 205 are made from solid polycrystallinediamond. This will completely eliminate any concern about the body'sacceptance of substrate metals, as none will be present. Solidpolycrystalline diamond components may be manufactured according to themethods presented below.

FIG. 2G depicts an alternative embodiment of the invention in which thecup 205 is made from a continuous or solid polycrystalline diamond (asopposed to a diamond table affixed to a substrate) and has been formedwith a porous region 233 including may small pores, cavities, openingsor fenestrations 234. The pores 234 permit the ingrowth of bone into thecup 205 so that osseointegration may be used as the fixation mechanismfor the cup, or osseointegration may be used in conjunction with anotherfixation mechanism such as press fitting. The pores 234 may be formed inthe cup by adding a quantity of beads or microspheres to the diamondfeedstock of the outer region of the cup prior to sintering. For optimalbone ingrowth, the pores will be sized in the range of 125 to 300microns. Generally it is expected that the pores will be in the range ofabout 50 to 500 microns in diameter. Beads or microspheres that may beused to form the pores include hexagonal boron nitride, cubic boronnitride, cobalt chrome, nickel and others. The beads or microspheres maybe chemically or mechanically removed from the polycrystalline diamondcompact matrix, leaving a porous surface suitable for biologicalfixation. Depending on the beads or microspheres used to form pores inthe cup, or other materials used in joint formation, it may be necessaryto chemically leach toxic materials out of the cup or prostheticcomponent before it can be implanted in a patient. Porous substrates maybe formed similarly. The ball 202 as depicted is also of solidpolycrystalline diamond, but no pores are provided in the ball, as itwill not be necessary to achieve bone ingrowth into the ball. Inalternative embodiments of the invention, any polycrystalline diamondcompact may be created with pores useful for biological fixation.

FIG. 2H depicts an acetabular cup assembly of the invention. Theassembly includes a shell 220 and a cup 221. The cup 221 is preferably asintered polycrystalline diamond compact having a substrate 222 and adiamond layer 223. The shell 220 may be affixed to patient bone 224 by avariety of attachment mechanisms, such as screws 220a, a nut and boltcombination 220 b, pins 220 c or threads 220 d on the shell 220.Adhesion and press fitting may also be used to affix the shell to bone.The shell may optionally include a textured bone-mating surface orappropriate coating (such as hydroxyl apatite) to encourage growngrowth, as discussed elsewhere herein. The acetabular cup may beattached to the shell according to a desired angular orientation andoffset during surgery in order to approximate natural joint geometry,such as shown in FIGS. 2H and 2I, or by another means.

FIG. 2I depicts a restrained acetabular cup assembly of the invention.The assembly may include the cup, shell and attachment mechanisms ofFIG. 2H. In addition, the assembly includes a retaining ring 225. Therestraining ring 225 is preferably an annular ring of polycrystallinediamond compact having a substrate layer 226 and a diamond table 227.The retaining ring 225 may include a number of bores 228 through it sothat fasteners 229 may be used to affix the ring 225 to the shell 220.The ring 225 would hold the cup 221 in the shell and would preventdislocation of a ball from the cup.

FIG. 2J depicts another acetabular cup assembly of the invention. Theassembly includes a polycrystalline diamond compact cup 239 thatincludes a diamond table 240 sintered to a substrate 241. A speciallyconfigured bone-mating surface 242 is provided on the hipbone side ofthe cup. The bone-mating surface may include a variety of structures inorder to aid in securing the cup 239 to a hipbone. The bone matingsurface 242 may include small pores to encourage bone growth thereto andtherein. Such small pores may be created by a titanium plasma spray ordiffusion bonding of beads or mesh, chemical leaching, laser machiningor other methods. The bone-mating surface 242 may also incorporate anapatite coating such as hydroxyl apatite to encourage bone growth.Hydroxyl apatite is applied in a thin coating with a high degree ofcrystalinity. The body will lay down protein structures next to theapatite to begin bone growth. The bone-mating surface 242 may alsoinclude small beads or other surface roughness such as ribbing to whichbone will grow. Surface Toughness that allows bone growth next to it canachieve osseointegration. Alternatively, the bone mating surface 242 maybe a porous metal mesh as is known in the medical art to promote bonegrowth. Appropriate metal meshes can be layers of titanium screendiffusion bonded together and then diffusion bonded to the metal of theprosthetic cup.

In such a configuration, a press fit, a wedge fit or another mechanicalor friction fit may be used to affix the prosthetic joint to a humanbone at the time of surgery. Press fitting is achieved by creating areceptacle in the bone slightly smaller than the prosthetic implant tobe used. Then the implant is forcefully inserted into the receptacle andis frictionally held there for immediate fixation. Alternatively,fixation of the prosthetic joint to bone can be achieved by use ofbolts, screws, rivets or pins, similar to those already discussed. Theprosthetic joint can also be attached to bone by use of an appropriateadhesive or cement, such as polymethyl methacrylate. Long-term fixationis provided or enhanced, however, by bone ingrowth into the bone matingsurface 242. Bone ingrowth will minimize micromovement of the jointduring use and will provide a more durable system for the patient. Whenapatite coatings are used, the bone will be encouraged to anchordirectly to the implant surface.

FIG. 2K depicts a prosthetic hip joint of the invention. It includes acup assembly 231 and a ball assembly 232. The ball assembly 232 includesstem 232 awhich may include a grooved or ridged portion 232 b and whichmay include a textured or coated portion 232 c. The ball assembly 232also includes a ball 232 d attached to the stem 232 a by a neck 232 e.The ball preferably provides a load bearing and articulation surfacethat is at least partially comprised of polycrystalline diamond, and asdesired the ball can be solid polycrystalline diamond. The cup assembly231 includes a shell 231 a, which may be attached to bone by mechanicalfasteners 231 b, by adhesion or by press fitting. The shell 231 a mayinclude a textured surface or bone growth-enhancing coating 231 c on itsexterior. An acetabular cup 231 d is mounted in the shell. Theacetabular cup 231 d as depicted includes a substrate 231 e and apolycrystalline diamond load bearing and articulation surface 231 f forproviding articulation with respect to the ball 232 d.

Referring to FIG. 2L, a femoral portion of a prosthetic hip joint of theinvention is depicted. It includes an integral stem and body 288, thestem portion of which may include ridges or grooves 289 for bonefixation, and the body of which may include a bone mating surface 290.The bone mating surface 290 may be a region of microtexture or poroussurface, a region of ribs, a metal mesh, shoulders or other appropriatetexture, a coating such as hydroxyl apatite or other apatite coating, orany other surface or feature that will encourage bone growth or bonefixation. The microtexture, porous surface, ribs or shoulders areintended to facilitate frictional engagement with human bone and topermit bone to grow adjacent thereto. In the case of a porous surface,it is intended that there may be osseointegration between the bone andthe surface in order to secure the implant to the bone. A porous surfacemay be achieved by placing small metal beads, balls or microspheres(such as metal balls of commercially pure titanium or a titanium alloycontaining 90% titanium, 6% aluminum and 4% vanadium) on the exterior ofthe prosthetic joint. The stem and body device 288 includes a mountingpole 291 for mounting a femoral head 292 thereto. The femoral head 292is a polycrystalline diamond compact that includes a substrate and apolycrystalline diamond bearing surface. A substrate protrusion 293 ispresent on the femoral head 292 in order to facilitate mounting of thefemoral head to the mounting pole, such as by welding or mechanicalfixation.

Referring to FIG. 2M, an example of an embodiment of the inventionemployed in a modular prosthetic hip assembly is depicted. The assemblyincludes an elongate stem 253 that has an elongate and rounded distalend 254 for insertion into an intermedullary channel of a femur. At theproximal end of the stem 253, an enlarged body 254 is found. A femalereceptacle, seat or recess 255 is located near the proximal end of thestem on the enlarged body. The receptacle is oriented in a mannerdivergent from the longidutinal axis of the stem. The receptacle 255 maybe configured for locking other portions of a prosthetic joint thereto.As depicted, the receptacle has an oval taper in order to establish afirm and permanent taper press fit with the neck 256 of the joint.Alternatively, the receptacle may be threaded or have another shape topermit fixation of another joint component thereto. The head may befixed to the neck by a separate self-locking taper or by anotherappropriate means such as welding (including inertia welding).

For insertion into the receptacle 255, a neck 256 is provided. The neck256 has a proximal portion 257 for stem fixation, a mid body portion258, and a distal portion 259 for femoral head fixation. The proximalportion 257 as depicted has a male oval taper for press fitting with thereceptacle 255 of the stem 253. If the receptacle 255 had anotherfixation mechanism, such as threads, then the proximal portion 257 ofthe neck 256 would include a complementary fixation structure. Thedistal portion 259 of the neck 256 as depicted is frusto-conical inshape in order to be press fit into an appropriate receptacle, seat orrecess 260 in a femoral head 261. The femoral head 261 is preferably apolycrystalline diamond compact. The neck mid body 258 may becylindrically shaped or otherwise shaped and may be provided in avariety of lengths. The femoral head 261 includes a bearing surface 262that is polycrystalline diamond, according to the principles of theinvention.

The assembly depicted, including the stem, stem receptacle, neck, andfemoral head is useful for causing a universal prosthetic joint stem andfemoral head to fit in a wide variety of patients. This is accomplishedby providing a variety of necks of different lengths and angularoffsets. Use of a neck of an appropriate length and angular offsetallows the femoral head to be oriented in a desired position withrespect to the stem in order approximate positioning of the naturalfemoral head. Ordinarily, the angular offset of the neck proximal end ormale taper with respect to the longitudinal axis of the neck mid portionwill be varied in order to provide a product line that will fit manypatients. As the neck portion of the prosthetic joint includes a slightangular offset, it actually achieves two different geometries in theprosthetic joint. For any angular geometry that may be achieved by theprosthetic joint, if the neck is removed and reinstalled 180 degrees outof phase, a mirror image geometry is then achieved.

In FIG. 2M, an alternative neck and femoral head assembly 263 isdepicted. In this embodiment of the invention, a polycrystalline diamondcompact prosthetic femoral head 264 is provided with a fixed neck 265protruding from it. The neck 265 includes a male attachment element 266that as depicted has an oval taper for press fitting with the receptacle255 of the stem 253. Unitary head and neck assemblies 263 may besupplied by the prosthetic joint manufacturer in a variety of femoralhead diameters, a variety of neck lengths, and a variety of neck angularoffsets in order to permit surgeons to achieve a good dimensional andgeometric fit in a patient during surgery. Taper fitting of variousparts of a prosthetic joint to each other may be achieved by a varietyof tapers, such as oval tapers, round tapers, and others.

Referring to FIG. 2N, an alternative embodiment of the invention isdepicted. In this embodiment of the invention, a prosthetic hip jointassembly 265 is provided. The assembly 265 includes a stem 266 forinsertion into an intermedullary canal of a femur. The stem 266 includesthreads 267 on its proximal end for fixation to a body 268 portion. Thethreads 267 of the stem 266 may accommodate a nut 269 inserted through areceptacle 270 of the body 268 for fixation of the stem 266 thereto. Thebody 268 includes a second receptacle 271 with an axis oriented at adivergent angle with the longitudinal axis of the body. The secondreceptacle 271 includes threads in its interior for receiving a threadedbody attachment end 272 of a neck 273. The body attachment end 272 ofthe neck 273 may be oriented at an angular offset with respect to themid portion 274 of the neck. The neck 273 also includes a femoral headattachment end 275 for attaching a femoral head 276 thereto, such as byuse of a threaded receptacle 277 on the femoral head. The preferredfemoral head as depicted is a polycrystalline diamond compact. The stem266 and the body 268 may include an appropriate bone mating surface,such as hydroxyl apatite, a porous surface, a high friction surface,wire mesh, or other features to assist in anchoring the prosthetic jointin bone.

FIG. 20 depicts a top view of anterior and posterior offset that can beachieved using an oval taper with the invention. A receptacle 278 a in afirst prosthetic joint component 278 b is provided. The receptacle 278 ahas an oval taper of desired configuration. A second prosthetic jointcomponent 278 c is provided having a protrusion 278 d that has an ovaltaper corresponding to that of the receptacle 278 a. The secondprosthetic joint component 278 c may be attached to the first prostheticjoint component 278 b by use of the oval tapers. A neutralanterior/posterior offset may be achieved by use of the installationconfiguration indicated at 278 e. Rotation of the second prostheticjoint component about the longitudinal axis of its tapered protrusion278 d can be used to achieve anterior offset 278 f of posterior offset278 g. This can be accomplished because the tapered protrusion 278 d ofthe second joint component protrudes from a neck 278 h. The taperedprotrusion 278 d and the neck 278 h each have a longitudinal axis. Thetapered protrusion 278 d may be located on the neck 278 h so that thelongitudinal axes of the tapered protrusion 278 d and the neck 278 h areat an angle other than 180 degrees. When the tapered protrusion isinstalled in a receptacle, it can be installed so that the angularorientation of the tapered protrusion with respect to the neck providesan anterior or posterior offset as desired.

FIG. 2S, 2T and 2U depict a side view of vertical offset that can beachieved using an oval taper in the invention. A first prosthetic jointcomponent 279 a and a second prosthetic joint component 279 b areprovided. The first prosthetic joint component 279 a has a taperedreceptacle 279 c as already described. The receptacle has a longitudinalaxis. The second prosthetic joint component 279 b includes a taperedprotrusion 279 d on a neck 279 e. Each of the tapered protrusion 279 dand the neck 279 e have a longitudinal axis. The second prosthetic jointcomponent 279 b may be installed in the receptacle 279 c of the firstprosthetic joint component 279 a so that the longitudinal axis of thereceptacle 279 c, the tapered protrusion 279 d and the neck 279 ecoincide. This is considered the neutral position with no positive ornegative vertical offset, as depicted in FIG. 2S. FIG. 2T depicts thesecond prosthetic joint component 279 b installed in the receptacle 279c so that there is an angular offset between the longitudinal axis ofthe neck 279 e with respect to the longitudinal axis of the receptacle279 c. In this case, that provides positive vertical offset of thesecond joint component with respect to the first joint component. FIG.2U depicts the second prosthetic joint component 279 b installed in thereceptacle 279 c so that there is a different angular offset between thelongitudinal axis of the neck 279 e with respect to the longitudinalaxis of the receptacle 279 c than was seen in FIG. 2T. In this case,that provides negative vertical offset of the second joint componentwith respect to the first joint component.

In some instances it will be desired to replace only one half of a humanjoint with a prosthetic device, continuing to use the other half of thenatural joint in conjunction with the newly implanted prosthetic device.An example of this is hemiarthroplasty. Referring to FIG. 2P, anembodiment of the invention useful for hemiarthroplasty is shown. Aprosthetic femoral head member 243 is shown. A stem (now shown) may beincluded for fixation in a femur by any fixation method discussedherein. A neck is provided attached to a stem. A femoral head 247 ismounted to the neck 246. The femoral head is a polycrystalline diamondcompact, including a substrate 248 and a diamond table 249.

Consistent with the principles of hemiarthroplasty, the femoral headmember 243 has been installed into a patient's natural acetabular cup250 of his hip 251 so that the load-bearing surface of the diamond table249 of the femoral head 247 articulates against natural cartilage 252 ofthe natural acetabular cup 250. The labrum 244 a and 244 b and cotyloidnotch 245 are undisturbed. In some instance hemiarthroplasty ispreferred in order to avoid the trauma and healing associated withreplacing a natural acetabular cup with a prosthetic device. The femoralhead used for hemiarthroplasty may be spherical but will preferably beslightly aspherical. Use of an aspherical head promotes synovial fluidingress to the natural acetabular cup for both lubrication andnourishment. Asphericity of the head may be achieved during finishmachining, grinding and polishing of the head, or it may be achievedduring manufacture by design of the substrate and loading and sinteringof the diamond feedstock.

Referring to FIG. 2Q, an alternative embodiment of the invention isemployed for re-surfacing a femoral head. As depicted, the patient'sfemoral head has been re-surfaced with a prosthetic device and thepatient's acetabular cup has been replaced. Re-surfacing the femoralhead will allow preservation of as much of the patient's natural bone aspossible because only the articulation surface and some adjacent boneare replaced. When a femoral head is re-surfaced, it may articulateagainst a natural acetabular cup or against a prosthetic acetabular cup.A re-surfacing head may be fixed to bone with any suitable means,including cement, biological fixation, porous surfaces, mechanicalfasteners and otherwise. For fixation using porous surfaces, a porousmetal substrate may be used, or the head may be made entirely ofpolycrystalline diamond with a porous bone ingrowth surface. As depictedin FIG. 2Q, the femoral head resurface is solid polycrystalline diamondwith pores in the diamond to promote bone ingrowth and biologicalfixation.

In FIG. 2Q, the patient's natural femoral head 2000 has been shaped by asurgeon to an appropriate shape for relining, such as frusto-conical. Aprosthetic femoral head surface 2001 has been placed over thefrusto-conical attachment. The prosthetic femoral head surface 2001 is apolycrystalline diamond compact, including a diamond table 2001 asintered to a substrate 2001 b. The substrate 2001 b is formed to have areceptacle 2001 c suitable for receiving a shaped bone. The diamondtable 2001 a serves as an articulation and load-bearing surface.

As depicted in the figure, the patient's natural hip 2002 has beenfitted with a prosthetic acetabular cup 2003. The cup 2003 is apolycrystalline diamond compact, including a diamond table 2003 bsintered to a substrate 2003 a. The diamond table 2003 b and the diamondtable 2001 a articulate in sliding and rolling engagement with eachother. The cup 2003 as depicted has been installed in an acetabularshell 2008, which is fixed to the bone 2002 with fasteners such asscrews 2004. The shell has an internal cavity for receiving theacetabular cup bearing, and a securing member (not shown) used to securethe cup within the shell.

FIG. 2R depicts an alternative hemiarthroplasty procedure. A naturalfemoral head 2000 has been re-shaped by a surgeon to receive aprosthetic femoral head liner 2005. In this case, the femoral head linerdepicted is solid polycrystalline diamond with an appropriate receptacle2007 for accommodating the shaped bone. The polycrystalline diamond 2005forms a load bearing and articulation surface for articulating against apatient's natural cartilage 2006 found on his hip 2002. Use of such aconfiguration achieves maximum bone preservation, minimum patienttrauma, and maximum biocompatibility.

FIGS. 2V-2Z and 2AA-2AG depict examples of other prosthetic joints ofthe invention.

FIG. 2V depicts a prosthetic shoulder joint 2020 of the invention. Theparticular configuration depicted is a modular joint but a non-modularjoint, bi-angular, bi-polar or other shoulder joint could also beconstructed according to the invention. The shoulder joint 2020 includesa humeral stem 2021 which may optionally include grooves or ridges 2022,a coated or textured bone mating surface 2023 and other features. Ahumeral head 2024 is provided that as depicted includes apolycrystalline diamond compact with a substrate 2025 and apolycrystalline diamond load bearing and articulation surface 2026. Aglenoid component 2027 is depicted that includes a polycrystallinediamond compact providing a substrate 2029 supporting a polycrystallinediamond load bearing and articulation surface 2028.

FIG. 2W depicts an unconstrained elbow joint 2030 of the invention. Itincludes humeral portion 2031, radial portion 2032 and ulnar potion2033. These portions may be made from polycrystalline diamond compact orother preferred materials according to the invention. As depicted,humeral potion 2031, radial portion 2032 and ulnar portion 2033 eachinclude a substrate 2031 a, 2032 a and 2033 a and a diamond load bearingand articulation surface 2031 b, 2032 b and 2033 c, respectively.Constrained elbow joints and single compartment elbow joint componentsmay also be made according to the invention.

FIG. 2X depicts a wrist joint 2035 according to the invention. The joint2035 includes a first joint component 2036 and a second joint component2037. The first joint component 2036 includes a bone attachment potion2036 a for attachment to a patient's bone. Affixed to the boneattachment portion 2036 a is a substrate 2036 b and a polycrystallinediamond load bearing and articulation surface 2036 c comprising apolycrystalline diamond compact. The second joint component 2037includes a bone attachment potion 2037 a for attachment to a patient'sbone. Affixed to the bone attachment portion 2037 a is a substrate 2037b and a polycrystalline diamond load bearing and articulation surface2037 c comprising a polycrystalline diamond compact.

FIG. 2Y depicts a prosthetic thorombomandibular joint of the invention.It includes a ramus portion 2040 and a mandibular portion 2041. Theramus portion 2040 includes an attachment plate 204 a for attaching tobone. The ramus portion 2041 includes a concave meniscus that ispreferably a polycrystalline diamond compact having a substrate 2040 band a polycrystalline diamond load bearing and articulation surface 2040c. The mandibular portion 2041 includes an attachment plate 2041 a forattaching to bone. It also includes a convex condyle 2041 b that ispreferably a polycrystalline diamond compact having a substrate (notshown) and a table of polycrystalline diamond 2041 c thereon.

FIG. 2Z depicts an intervertebtral disc prosthesis 2050 of theinvention. The disk prosthesis 2050 includes a top disk member 2051, abottom disk member 2052 and a disk core 2053. The top disk member 2051and bottom disk member 2052 are preferably held together by cables 2054a and 2054 b or other attachment mechanisms to prevent overextension anddislocation. The top disk member 2051 includes a generally convexarticulation portion 2051 b. The articulation portion 2051 b includes apolycrystalline diamond load bearing and articulation surface 2051 cthat is part of a polycrystalline diamond compact including a substrate2051 a. The bottom disk member 2052 includes a generally convexarticulation portion 2052 b. The articulation portion 2052 b includes apolycrystalline diamond load bearing and articulation surface 2052 cthat is part of a polycrystalline diamond compact including a substrate2052 a. The two convex articulation portions form a cavity 2055 in whicha disk core 2052 is found. The disk core 2055 permits sliding androlling articulation of the top and bottom disk members with respectthereto. The disk core 2053 depicted includes a top convex articulationsurface 2053 a and a bottom convex articulation surface 2053 b that arepreferably polycrystalline diamond formed on a polycrystalline diamondcompact that includes a substrate 2053 c.

FIG. 2AA depicts a prosthetic joint useful in the carpometacaral jointin the thumb and in other areas of the body. The joint 2060 includes afirst joint component 2061 having a bone attachment portion such as pegsor pins 2061 a, a substrate 2061 b, and a table of polycrystallinediamond 2061 c which forms a load bearing and articulation surface.Opposing the first joint component 2061 is a second joint component2062. The second joint component includes a bone attachment portion 2062a, a substrate 2062 b, and a table of polycrystalline diamond 2062 c,which forms a load bearing and articulation surface for articulationagainst 2061 c.

FIGS. 2AB and 2AC depict a prosthetic knee joint of the invention fortotal knee replacement. The joint includes a tibial component 2010, afemoral component 2011 and a patella component 2012. Preferably, eachload bearing and articulation surface of the joint will be made fromsintered polycrystalline diamond or another preferred material of theinvention. As depicted, the tibial component includes a tray 2013 onwhich the load bearing and articulation portion 2014 is mounted. Thetray 2013 may be a substrate to which is sintered polycrystallinediamond compact to serve as the load bearing and articulation portion2014. Alternatively, the tray 2013 may be of the general configurationof those found in the prior art, and the load bearing and articulationportion 2014 may be solid polycrystalline diamond, a polycrystallinediamond compact including a substrate and a diamond table located on thesubstrate, or another appropriate load bearing and articulation surfacematerial. The femoral component 2011 is depicted as having a loadbearing and articulation surface 2015 located on a substrate 2016, butmight be constructed as described for the tibial portion 2010 orotherwise. A patella component 2012 is provided which may be apolycrystalline diamond compact including a diamond table 2017 and asubstrate 2018 or another structure as described herein.

FIGS. 2AD and 2AE depict side and front views, respectively, of aprosthetic joint useful for unicompartmental knee replacement. Thisjoint is useful for treating disease of a single knee compartment wherereplacement of the entire knee joint is not necessary. The joint 2100includes a femoral component 2101 with a polycrystalline diamond bearingsurface 2102 and a substrate 2103. The tibial component 2104 is a traywith an appropriately shaped slot or receptacle 2105 for receiving abearing insert 2106 therein. The slot 2105 permits anterior andposterior sliding motion in the joint. The bearing insert 2106 includesa protrusion 2107 for fitting in the slot 2105. The bearing insert 2106also includes a substrate 2108 on which is found a polycrystallinediamond bearing surface 2109.

FIGS. 2AF and 2AG depict front and side views, respectively, of asliding bearing rotating platform total knee joint 2030 of theinvention. The joint 2030 includes a tibial tray 2031 with a receptacletherein 2032 for accepting a rotating platform 2033. The rotatingplatform 2033 has a protrusion 2034 for fitting into the receptacle2032. The rotating platform 2033 accommodates rotational movement withinthe knee joint as indicated by arrows 2035 a and 2035 b. Sliding bearinginserts 2036 a and 2036 b fit into appropriately shaped slots in therotating platform 2033 and permit anterior and posterior sliding motionin the knee joint. The bearing inserts 2036 a and 2036 b preferablyinclude a diamond bearing surface 2037 a and 2037 b on a substrate 2038a and 2038 b. A femoral component 2039 is provided which also preferablyincludes a diamond bearing surface 2040 on a substrate 2041.

The various joints mentioned above and other joints (including ankle,interphalangeal, and other joints) made using embodiments of theinvention may be constructed in constrained and unconstrainedconfigurations. Multi-compartment joints (such as knees) may be treatedwith a uni-compartmental prosthetic joint of the invention of amulti-compartmental joint of the invention. Ball and socket joints,hinge joints, sliding joints and other joints may be made according tothe invention. In addition, all of the load bearing and articulationssurfaces of a prosthetic joint or any subset of them may be made from amaterial or structure of the invention or by a method of the invention.If only a subset of the load bearing and articulation surfaces of ajoint are made according to the invention, then the remaining portionsof the joint may be made from other materials described herein oraccording to the prior art. Partial joint replacements (such ashemiarthroplasty and uni-compartment knee replacement) may also beaccomplished using joint components of the invention. Prosthetic jointsof any desired configuration, in addition to those depicted anddiscussed herein may be made according to the invention. Principles ofthe invention may be employed regardless of whether the joint is modularor non-modular, or whether an entire joint, a single joint component, oronly an articulation surface is being manufactured.

C. Dimensions and Geometry of Preferred Joints

In the preferred hip joint of the invention, the ball includes at leasta portion of a convex sphere and the socket includes at least a portionof a concave sphere. The spherically shaped portions of the ball andsocket are preferably of similar radius so as to fit together withrequired tolerances. Appropriate tolerances for hard-hard bearingsurfaces are known to persons of skill in the art. Very similar radiusesare desired for the cup and ball in a prosthetic hip joint so that theywill entrain fluid for lubrication. It is also desired to utilize a cupand ball of similar radius in order to minimize stress fields for thearticulation surface. In some preferred embodiments of the invention,the sphere on which the ball and socket spherical portions are based isa sphere that has a radius of about from less than 22 millimeters tomore than about 60 millimeters. In a prosthetic joint, it is desirableto use the largest possible geometry that the patient's anatomy willpermit in order to achieve the greatest range of motion and mechanicalstrength in excess of the supporting bone structures.

In those embodiments of the invention that include a diamond table onone of the articulation surfaces, the diamond table will typically befrom submicron thickness to about 3000 microns thick or more. Someembodiments of the invention utilize a solid polycrystalline diamondcomponent, such as a solid polycrystalline diamond ball or a solidpolycrystalline diamond socket. In those cases, the diamond tabledimension will equal the component dimension.

For ball and socket joints using a polycrystalline diamond compact witha substrate, it is expected that for ease of manufacturing, thepolycrystalline diamond table will be from less than about 5 micronsthick to more than about 2 millimeters thick in the most preferredembodiments of the invention. Other diamond joint surfaces might havethickness in the range of less than about 1 micron to more than about100 microns, or solid polycrystalline diamond components could be usedas described above.

Both the ball and cup should be as close to spherical as manufacturingand finishing processes allow. This will maximize the contact surfacearea of the ball and cup, in order to diffuse the contact load and tomaximize wear life of the joint. It is also preferred that the ball haveat least 180 degrees of articulating surface for rotation in the socketin order to approximate the range of motion of a natural joint.

In hemiarthroplasty, a small degree of asphericity may be desirable inorder to promote ingress of synovial fluid, providing lubrication andnutrition to the cartilage counter-bearing surface.

In various embodiments of the invention, the geometry and dimensions ofthe bearing surface of the component may be designed to meet the needsof a particular application and may differ from that which is describedabove.

E. Attachment of Diamond in the Preferred Joint

1. Nature of the Diamond-Substrate Interface

In prior art prosthetic joints, a polyethylene articulation surface wascemented to a cup or mechanically fixed to a shell, such as by use offlanges, a locking ring, or tabs. Alternatively, the polyethylenearticulation surface was injection molded onto an appropriate metalsurface. None of the prior art provided a prosthetic joint with adiamond table articulation surface, a sintered polycrystalline diamondcompact, or the transition zone of the invention.

In the preferred embodiment of the invention, a polycrystalline diamondcompact provides unique chemical bonding and mechanical grip between thearticulation surface and the substrate material, as compared to priorart cementing or mechanical fixation of a polyethylene articulationsurface.

Some preferred prosthetic joint structures of the invention uses apolycrystalline diamond compact for at least one of the femoral headand/or the acetabular cup. A polycrystalline diamond compact, whichutilizes a substrate material, will have a chemical bond betweensubstrate material and the diamond crystals. The result of thisstructure is an extremely strong bond between the substrate and thediamond table.

A method by which PDC is preferably manufactured is described later inthis document. Briefly, it involves sintering diamond crystals to eachother, and to a substrate under high pressure and high temperature.FIGS. 4A and 4B illustrate the physical and chemical processes involvedmanufacturing polycrystalline diamond compacts.

In FIG. 4A, a quantity of diamond feedstock 430 (such as diamond powderor crystals) is placed adjacent to a metal-containing substrate 410prior to sintering. In the region of the diamond feedstock 430,individual diamond crystals 431 may be seen, and between the individualdiamond crystals 431 there are interstitial spaces 432. If desired, aquantity of solvent-catalyst metal may be placed into the interstitialspaces 432.

The substrate 410 may be a suitable pure metal or alloy, or a cementedcarbide containing a suitable metal or alloy as a cementing agent suchas cobalt-cemented tungsten carbide. Preferably the substrate will be ametal with high tensile strength. In the preferred cobalt-chromesubstrate of the invention, the cobalt-chrome alloy will serve as asolvent-catalyst metal for solvating diamond crystals during thesintering process.

The illustration shows the individual diamond crystals and thecontiguous metal crystals in the metal substrate. The interface 420between diamond powder and substrate material is a critical region wherebonding of the diamond table to the substrate must occur. In someembodiments of the invention, a boundary layer of a third materialdifferent than the diamond and the substrate is placed at the interface420. This interface boundary layer material, when present, may serveseveral functions including, but not limited to, enhancing the bond ofthe diamond table to the substrate, and mitigation of the residualstress field at the diamond-substrate interface.

Once diamond powder or crystals and substrate are assembled as shown inFIG. 4A, the assembly is subjected to high pressure and high temperatureas described later herein in order to cause bonding of diamond crystalsto diamond crystals and to the substrate. The resulting structure ofsintered polycrystalline diamond table bonded to a substrate is called apolycrystalline diamond compact (PDC). A compact, as the term is usedherein, is a composite structure of two different materials, such asdiamond crystals, and a substrate metal. The analogous structureincorporating cubic boron nitride crystals in the sintering processinstead of diamond crystals is called polycrystalline cubic boronnitride compact (PCBNC). Many of the processes described herein for thefabrication and finishing of PDC structures and parts work in a similarfashion for PCBNC. In some embodiments of the invention, PCBNC may besubstituted for PDC.

FIG. 4B depicts a polycrystalline diamond compact 401 after the highpressure and high temperature sintering of diamond feedstock to asubstrate. Within the PDC structure, there is an identifiable volume ofsubstrate 402, an identifiable volume of diamond table 403, and atransition zone 404 between diamond table and substrate containingdiamond crystals and substrate material. Crystalline grains of substratematerial 405 and sintered crystals of diamond 406 are depicted.

On casual examination, the finished compact of FIG. 4B will appear toconsist of a solid table of diamond 403 attached to the substrate 402with a discrete boundary. On very close examination, however, atransition zone 404 between diamond table 403 and substrate 402 can becharacterized. This zone represents a gradient interface between diamondtable and substrate with a gradual transition of ratios between diamondcontent and metal content. At the substrate side of the transition zone,there will be only a small percentage of diamond crystals and a highpercentage of substrate metal, and on the diamond table side, there willbe a high percentage of diamond crystals and a low percentage ofsubstrate metal. Because of this gradual transition of ratios ofpolycrystalline diamond to substrate metal in the transition zone, thediamond table and the substrate have a gradient interface.

In the transition zone where diamond crystals and substrate metal areintermingled, chemical bonds are formed between the diamond and metal.From the transition zone 404 into the diamond table 403, the metalcontent diminishes and is limited to solvent-catalyst metal that fillsthe three-dimensional vein-like structure of interstitial voids oropenings 407 within the sintered diamond table structure 403. Thesolvent-catalyst metal found in the voids or openings 407 may have beenswept up from the substrate during sintering or may have beensolvent-catalyst metal added to the diamond feedstock before sintering.

During the sintering process, there are three types of chemical bondsthat are created: diamond-to-diamond bonds, diamond-to-metal bonds, andmetal-to-metal bonds. In the diamond table, there are diamond-to-diamondbonds (sp3 carbon bonds) created when diamond particles partiallysolvate in the solvate-catalyst metal and then are bonded together. Inthe substrate and in the diamond table, there are metal-to-metal bondscreated by the high pressure and high temperature sintering process. Andin the gradient transition zone, diamond-to-metal bonds are createdbetween diamond and solvent-catalyst metal.

The combination of these various chemical bonds and the mechanical gripexerted by solvent-catalyst metal in the diamond table such as in theinterstitial spaces of the diamond structure diamond table provideextraordinarily high bond strength between the diamond table and thesubstrate. Interstitial spaces are present in the diamond structure andthose spaces typically are filled with solvent-catalyst metal, formingveins of solvent-catalyst metal within the polycrystalline diamondstructure. This bonding structure contributes to the extraordinaryfracture toughness of the compact, and the veins of metal within thediamond table act as energy sinks halting propagation of incipientcracks within the diamond structure. The transition zone and metal veinstructure provide the compact with a gradient of material propertiesbetween those of the diamond table and those of substrate material,further contributing to the extreme toughness of the compact. Thetransition zone can also be called an interface, a gradient transitionzone, a composition gradient zone, or a composition gradient, dependingon its characteristics. The transition zone distributesdiamond/substrate stress over the thickness of the zone, reducing zonehigh stress of a distinct linear interface. The subject residual stressis created as pressure and temperature are reduced at the conclusion ofthe high pressure/high temperature sintering process due to thedifference in pressure and thermal expansive properties of the diamondand substrate materials.

The diamond sintering process occurs under conditions of extremely highpressure and high temperature. According to the inventors bestexperimental and theoretical understanding, the diamond sinteringprocess progresses through the following sequence of events. Atpressure, a cell containing feedstock of unbonded diamond powder orcrystals (diamond feedstock) and a substrate is heated to a temperatureabove the melting point of the substrate metal 410 and molten metalflows or sweeps into the interstitial voids 407 between the adjacentdiamond crystals 406. It is carried by the pressure gradient to fill thevoids as well as being pulled in by the surface energy or capillaryaction of the large surface area of the diamond crystals 406. As thetemperature continues to rise, carbon atoms from the surface of diamondcrystals dissolve into this interstitial molten metal, forming a carbonsolution.

At the proper threshold of temperature and pressure, diamond becomes thethermodynamically favored crystalline allotrope of carbon. As thesolution becomes super saturated with respect to C_(d) (carbon diamond),carbon from this solution begins to crystallize as diamond onto thesurfaces of diamond crystals bonding adjacent diamond crystals togetherwith diamond-diamond bonds into a sintered polycrystalline diamondstructure 406. The interstitial metal fills the remaining void spaceforming the vein-like lattice structure 407 within the diamond table bycapillary forces and pressure driving forces. Because of the crucialrole that the interstitial metal plays in forming a solution of carbonatoms and stabilizing these reactive atoms during the diamondcrystallization phase in which the polycrystalline diamond structure isformed, the metal is referred to as a solvent-catalyst metal.

FIG. 4BB depicts a polycrystalline diamond compact having both substratemetal 480 and diamond 481, but in which there is a continuous gradienttransition 482 from substrate metal to diamond. In such a compact, thegradient transition zone may be the entire compact.

In some embodiments of the invention, a quantity of solvent-catalystmetal may be combined with the diamond feedstock prior to sintering.This is found to be necessary when forming thick PCD tables, solid PDCstructures, or when using multimodal fine diamond where there is littleresidual free space within the diamond powder. In each of these cases,there is insufficient ingress of solvent-catalyst metal via the sweepmechanism to adequately mediate the sintering process as asolvent-catalyst. The metal may be added by direct addition of powder,or by generation of metal powder in situ with an attritor mill or by thewell-known method of chemical reduction of metal salts deposited ondiamond crystals. Added metal may constitute any amount from less than1% by mass, to greater than 35%. This added metal may consist of thesame metal or alloy as is found in the substrate, or may be a differentmetal or alloy selected because of its material and mechanicalproperties. Example ratios of diamond feedstock to solvent-catalystmetal prior to sintering include mass ratios of 70:30, 85:15, 90:10, and95:15. The metal in the diamond feedstock may be added powder metal,metal added by an attritor method, vapor deposition or chemicalreduction of metal into powder.

When sintering diamond on a substrate with an interface boundary layer,no solvent-catalyst metal from the substrate is available to sweep intothe diamond table and participate in the sintering process. In thiscase, the boundary layer material, if composed of a suitable material,metal or alloy that can function as a solvent-catalyst, may serve as thesweep material mediating the diamond sintering process. In other caseswhere the desired boundary material cannot serve as a solvent-catalyst,a suitable amount of solvent-catalyst metal powder as described hereinis added to the diamond crystal feed stock as described above. Thisassembly is then taken through the sintering process. In the absence ofa substrate metal source, the solvent-catalyst metal for the diamondsintering process must be supplied entirely from the added metal powder.The boundary material bonds chemically to the substrate material, andbonds chemically to the diamond table and/or the added solvent-catalystmetal in the diamond table. The remainder of the sintering andfabrication process are the same as with the conventionalsolvent-catalyst sweep sintering and fabrication process.

For the sake of simplicity and clarity in this patent, the substrate,transition zone, and diamond table have been discussed as distinctlayers. However, it is important to realize that the finished sinteredobject consists of a composite structure characterized by a continuousgradient transition from substrate material to diamond table rather thanas distinct layers with clear and discrete boundaries, hence the term“compact”.

In addition to the sintering processes described above, diamond partssuitable for use as bearings for such applications as total hips mayalso be fabricated as solid polycrystalline diamond structures without asubstrate. These are formed by placing the diamond powder combined witha suitable amount of added solvent-catalyst metal powder as describedabove in a refractory metal can (typically Ta, Nb, Zr, or Mo) with ashape approximating the shape of the final part desired. This assemblyis then taken through the sintering process. However, in the absence ofa substrate metal source, the solvent-catalyst metal for the diamondsintering process must be supplied entirely from the added metal powder.With suitable finishing, objects thus formed may be used as is, orbonded to metal substrates to function as total joint articulations.

Sintering is the preferred method of creating a diamond table with astrong and durable bond to a substrate material. Other methods ofproducing a diamond table bonded to a substrate are possible. Atpresent, these typically are not as strong or durable as thosefabricated with the sintering process. It is also possible to use thesemethods to form diamond structures directly onto substrates suitable foruse as prosthetic joint bearings. A table of polycrystalline diamondeither with or without a substrate may be manufactured and laterattached to a prosthetic joint in a location such that it will form abearing surface. The attachment could be performed with any suitablemethod, including welding, brazing, sintering, diffusion welding,diffusion bonding, inertial welding, adhesive bonding, or the use offasteners such as screws, bolts, or rivets. In the case of attaching adiamond table without a substrate to another object, the use of suchmethods as brazing, diffusion welding/bonding or inertia welding may bemost appropriate.

2. Alternative Methods for Creating a Diamond Bearing Surface

Although high pressure/high temperature sintering is the preferredmethod for creating a diamond bearing surface, other methods forproducing a volume of diamond may be employed as well. For example,either chemical vapor deposition (CVD), or physical vapor deposition(PVD) processes may be used. CVD produces a diamond layer by thermallycracking an organic molecule and depositing carbon radicals on asubstrate. PVD produces a diamond layer by electrically causing carbonradicals to be ejected from a source material and to deposit on asubstrate where they build a diamond crystal structure.

The CVD and PVD processes have some advantages over sintering. Sinteringis performed in large, expensive presses at high pressure (such as 45-68kilobars) and at high temperatures (such as 1200 to 1500 degreesCelsius). It is difficult to achieve and maintain desired componentshape using a sintering process because of flow of high pressure mediumsused and possible deformation of substrate materials.

In contrast, CVD and PVD take place at atmospheric pressure or lower, sothere no need for a pressure medium and there is no deformation ofsubstrates.

Another disadvantage of sintering is that it is difficult to achievesome geometries in a sintered polycrystalline diamond compact. When CVDor PVD are used, however, the gas phase used for carbon radicaldeposition can completely conform to the shape of the object beingcoated, making it easy to achieve a desired non-planar shape.

Another potential disadvantage of sintering polycrystalline diamondcompacts is that the finished component will tend to have large residualstresses caused by differences in the coefficient of thermal expansionand modulus between the diamond and the substrate. While residualstresses can be used to improve strength of a part, they can also bedisadvantageous. When CVD or PVD is used, residual stresses can beminimized because CVD and PVD processes do not involve a significantpressure transition (such from 68 Kbar to atmospheric pressure in highpressure and high temperature sintering) during manufacturing.

Another potential disadvantage of sintering polycrystalline diamondcompacts is that few substrates have been found that are suitable forsintering. In the prior art, the typical substrate used was tungstencarbide. In the invention, non-planar components have been made usingother substrates. When CVD or PVD are used, however, synthetic diamondcan be placed on many substrates, including titanium, most carbides,silicon, molybdenum and others. This is because the temperature andpressure of the CVD and PVD coating processes are low enough thatdifferences in coefficient of thermal expansion and modulus betweendiamond and the substrate are not as critical as they are in a hightemperature and high pressure sintering process.

A further difficulty in manufacturing sintered polycrystalline diamondcompacts is that as the size of the part to be manufactured increases,the size of the press must increase as well. Sintering of diamond willonly take place at certain pressures and temperatures, such as thosedescribed herein. In order to manufacture larger sinteredpolycrystalline diamond compacts, ram pressure of the press (tonnage)and size of tooling (such as dies and anvils) must be increased in orderto achieve the necessary pressure for sintering to take place. Butincreasing the size and capacity of a press is more difficult thansimply increasing the dimensions of its components. There may be apractical physical size constraints on press size due to themanufacturing process used to produce press tooling.

Tooling for a press is typically made from cemented tungsten carbide. Inorder to make tooling, the cemented tungsten carbide is sintered in avacuum furnace followed by pressing in a hot isosatic press (“HIP”)apparatus. Hipping must be performed in a manner that maintains uniformtemperature throughout the tungsten carbide in order to achieve uniformphysical qualities and quality. These requirements impose a practicallimit on the size tooling that can be produced for a press that isuseful for sintering polycrystalline diamond compacts. The limit on thesize tooling that can be produced also limits the size press that can beproduced.

CVD and PVD manufacturing apparatuses may be scaled up in size with fewlimitations, allowing them to produce polycrystalline diamond compactsof almost any desired size.

CVD and PVD processes are also advantageous because they permit precisecontrol of the thickness and uniformity of the diamond coating to beapplied to a substrate. Temperature is adjusted within the range of 500to 1000 degrees Celsius, and pressure is adjusted in a range of lessthan 1 atmosphere to achieve desired diamond coating thickness.

Another advantage of CVD and PVD processes is that they allow themanufacturing process to be monitored as it progresses. A CVD or PVDreactor can be opened before manufacture of a part is completed so thatthe thickness and quality of the diamond coating being applied to thepart may be determined. From the thickness of the diamond coating thathas already been applied, time to completion of manufacture can becalculated. Alternatively, if the coating is not of desired quality, themanufacturing processes may be aborted in order to save time and money.

In contrast, sintering of polycrystalline diamond compacts is performedas a batch process that cannot be interrupted, and progress of sinteringcannot be monitored. The pressing process must be run to completion andthe part may only be examined afterward.

CVD is performed in an apparatus called a reactor. A basic CVD reactorincludes four components. The first component of the reactor is one ormore gas inlets. Gas inlets may be chosen based on whether gases arepremixed before introduction to the chamber or whether the gases areallowed to mix for the first time in the chamber. The second componentof the reactor is one or more power sources for the generation ofthermal energy. A power source is needed to heat the gases in thechamber. A second power source may be used to heat the substratematerial uniformly in order to achieve a uniform coating of diamond onthe substrate. The third component of the reactor is a stage or platformon which a substrate is placed. The substrate will be coated withdiamond during the CVD process. Stages used include a fixed stage, atranslating stage, a rotating stage and a vibratory stage. Anappropriate stage must be chosen to achieved desired diamond coatingquality and uniformity. The fourth component of the reactor is an exitport for removing exhaust gas from the chamber. After gas has reactedwith the substrate, it must be removed from the chamber as quickly aspossible so that it does not participate in other reactions, which wouldbe deleterious to the diamond coating.

CVD reactors are classified according to the power source used. Thepower source is chosen to create the desired species necessary to carryout diamond thin film deposition. Some CVD reactor types includeplasma-assisted microwave, hot filament, electron beam, single, doubleor multiple laser beam, arc jet and DC discharge. These reactors differin the way they impart thermal energy to the gas species and in theirefficiency in breaking gases down to the species necessary fordeposition of diamond. It is possible to have an array of lasers toperform local heating inside a high pressure cell. Alternatively, anarray of optical fibers could be used to deliver light into the cell.

The basic process by which CVD reactors work is as follows. A substrateis placed into the reactor chamber. Reactants are introduced to thechamber via one or more gas inlets. For diamond CVD, methane (CH₄) andhydrogen (H₂) gases are preferably brought into the chamber in premixedform. Instead of methane, any carbon-bearing gas in which the carbon hassp3 bonding may be used. Other gases may be added to the gas stream inorder to control quality of the diamond film, deposition temperature,gain structure and growth rate. These include oxygen, carbon dioxide,argon, halogens and others.

The gas pressure in the chamber is preferably maintained at about 100torr. Flow rates for the gases through the chamber are preferably about10 standard cubic centimeters per minute for methane and about 100standard cubic centimeters per minute for hydrogen. The composition ofthe gas phase in the chamber is preferably in the range of 90-99.5%hydrogen and 0.5-10% methane.

When the gases are introduced into the chamber, they are heated. Heatingmay be accomplished by many methods. In a plasma-assisted process, thegases are heated by passing them through a plasma. Otherwise, the gasesmay be passed over a series of wires such as those found in a hotfilament reactor.

Heating the methane and hydrogen will break them down into various freeradicals. Through a complicated mixture of reactions, carbon isdeposited on the substrate and joins with other carbon to formcrystalline diamond by sp3 bonding. The atomic hydrogen in the chamberreacts with and removes hydrogen atoms from methyl radicals attached tothe substrate surface in order to create molecular hydrogen, leaving aclear solid surface for further deposition of free radicals.

If the substrate surface promotes the formation of sp2 carbon bonds, orif the gas composition, flow rates, substrate temperature or othervariables are incorrect, then graphite rather than diamond will grow onthe substrate.

There are many similarities between CVD reactors and processes and PVDreactors and processes. PVD reactors differ from CVD reactors in the waythat they generate the deposition species and in the physicalcharacteristics of the deposition species. In a PVD reactor, a plate ofsource material is used as a thermal source, rather than having aseparate thermal source as in CVD reactors. A PVD reactor generateselectrical bias across a plate of source material in order to generateand eject carbon radicals from the source material. The reactor bombardsthe source material with high energy ions. When the high energy ionscollide with source material, they cause ejection of the desired carbonradicals from the source material. The carbon radicals are ejectedradially from the source material into the chamber. The carbon radicalsthen deposit themselves onto whatever is in their path, including thestage, the reactor itself, and the substrate.

Referring to FIG. 4C, a substrate 440 of appropriate material isdepicted having a deposition face 441 on which diamond may be depositedby a CVD or PVD process. FIG. 4D depicts the substrate 440 and thedeposition face 441 on which a volume of diamond 442 has been depositedby CVD or PVD processes. A small transition zone 443 is present in whichboth diamond and substrate are located. In comparison to FIG. 4B, it canbe seen that the CVD or PVD diamond deposited on a substrate lacks themore extensive gradient transition zone of sintered polycrystallinediamond compacts because there is no sweep of solvent-catalyst metalthrough the diamond table in a CVD or PVD process.

Both CVD and PVD processes achieve diamond deposition by line of sight.Means (such as vibration and rotation) are provided for exposing alldesired surfaces for diamond deposition. If a vibratory stage is to beused, the bearing surface will vibrate up and down with the stage andthereby present all bearing surfaces to the free radical source.

There are several methods, which may be implemented in order to coatcylindrical objects with diamond using CVD or PVD processes. If a plasmaassisted microwave process is to be used to achieve diamond deposition,then the object to receive the diamond must be directly under the plasmain order to achieve the highest quality and most uniform coating ofdiamond. A rotating or translational stage may be used to present everyaspect of the bearing surface to the plasma for diamond coating. As thestage rotates or translates, all portions of the bearing surface may bebrought directly under the plasma for coating in such a way to achievesufficiently uniform coating.

If a hot filament CVD process is used, then the bearing surface shouldbe placed on a stationary stage. Wires or filaments (typically tungsten)are strung over the stage so that their coverage includes the bearingsurface to be coated. The distance between the filaments and the bearingsurface and the distance between the filaments themselves may be chosento achieve a uniform coating of diamond directly under the filaments.

Diamond bearing surfaces can be manufactured by CVD and PVD processeither by coating a substrate with diamond or by creating a freestanding volume of diamond, which is later mounted for use. A freestanding volume of diamond may be created by CVD and PVD processes in atwo-step operation. First, a thick film of diamond is deposited on asuitable substrate, such as silicon, molybdenum, tungsten or others.Second, the diamond film is released from the substrate.

As desired, segments of diamond film may be cut away, such as by use ofa Q-switched YAG laser. Although diamond is transparent to a YAG laser,there is usually a sufficient amount of sp2 bonded carbon (as found ingraphite) to allow cutting to take place. If not, then a line may bedrawn on the diamond film using a carbon-based ink. The line should besufficient to permit cutting to start, and once started, cutting willproceed slowly.

After an appropriately-sized piece of diamond has been cut from adiamond film, it can be attached to a desired object in order to serveas a bearing surface. For example, the diamond may be attached to asubstrate by welding, diffusion bonding, adhesion bonding, mechanicalfixation or high pressure and high temperature bonding in a press.

Although CVD and PVD diamond on a substrate do not exhibit a gradienttransition zone that is found in sintered polycrystalline diamondcompacts, CVD and PVD process can be conducted in order to incorporatemetal into the diamond table. As mentioned elsewhere herein,incorporation of metal into the diamond table enhances adhesion of thediamond table to its substrate and can strengthen the polycrystallinediamond compact. Incorporation of diamond into the diamond table can beused to achieve a diamond table with a coefficient of thermal expansionand compressibility different from that of pure diamond, andconsequently increasing fracture toughness of the diamond table ascompared to pure diamond. Diamond has a low coefficient of thermalexpansion and a low compressibility compared to metals. Therefore thepresence of metal with diamond in the diamond table achieves a higherand more metal-like coefficient of thermal expansion and the averagecompressibility for the diamond table than for pure diamond.Consequently, residual stresses at the interface of the diamond tableand the substrate are reduced, and delamination of the diamond tablefrom the substrate is less likely.

A pure diamond crystal also has low fracture toughness. Therefore, inpure diamond, when a small crack is formed, the entire diamond componentfails catastrophically. In comparison, metals have a high fracturetoughness and can accommodate large cracks without catastrophic failure.Incorporation of metal into the diamond table achieves a greaterfracture toughness than pure diamond. In a diamond table havinginterstitial spaces and metal within those interstitial spaces, if acrack forms in the diamond and propagates to an interstitial spacecontaining metal, the crack will terminate at the metal and catastrophicfailure will be avoided. Because of this characteristic, a diamond tablewith metal in its interstitial spaces is able to sustain much higherforces and workloads without catastrophic failure compared to purediamond.

Diamond-diamond bonding tends to decrease as metal content in thediamond table increases. CVD and PVD processes can be conducted so thata transition zone is established. However, it is preferred for thebearing surface to be essentially pure polycrystalline diamond for lowwear properties.

Generally CVD and PVD diamond is formed without large interstitialspaces filled with metal. Consequently, most PVD and CVD diamond is morebrittle or has a lower fracture toughness than sintered polycrystallinediamond compacts. CVD and PVD diamond may also exhibit the maximumresidual stresses possible between the diamond table and the substrate.It is possible, however, to form CVD and PVD diamond film that has metalincorporated into it with either a uniform or a functionally gradientcomposition.

One method for incorporating metal into a CVD or PVD diamond film it touse two different source materials in order to simultaneously depositthe two materials on a substrate in a CVD of PVD diamond productionprocess. This method may be used regardless of whether diamond is beingproduced by CVD, PVD or a combination of the two.

Another method for incorporating metal into a CVD diamond film chemicalvapor infiltration. This process would first create a porous layer ofmaterial, and then fill the pores by chemical vapor infiltration. Theporous layer thickness should be approximately equal to the desiredthickness for either the uniform or gradient layer. The size anddistribution of the pores can be sued to control ultimate composition ofthe layer. Deposition in vapor infiltration occurs first at theinterface between the porous layer and the substrate. As depositioncontinues, the interface along which the material is deposited movesoutward from the substrate to fill pores in the porous layer. As thegrowth interface moves outward, the deposition temperature along theinterface is maintained by moving the sample relative to a heater or bymoving the heater relative to the growth interface. It is imperativethat the porous region between the outside of the sample and the growthinterface be maintained at a temperature that does not promotedeposition of material (either the pore-filling material or undesiredreaction products). Deposition in this region would close the poresprematurely and prevent infiltration and deposition of the desiredmaterial in inner pores. The result would be a substrate with openporosity an poor physical properties.

Another alternative manufacturing process that may be used to producebearing surfaces and components of the invention involves use of energybeams, such as laser energy, to vaporize constituents in a substrate andredeposit those constituents on the substrate in a new form, such as inthe form of a diamond coating. As an example, a metal, polymeric orother substrate may be obtained or produced containing carbon, carbidesor other desired constituent elements. Appropriate energy, such as laserenergy, may be directed at the substrate to cause constituent elementsto move from within the substrate to the surface of the substrateadjacent the area of application of energy to the substrate. Continuedapplication of energy to the concentrated constituent elements on thesurface of the substrate can be used to cause vaporization of some ofthose constituent elements. The vaporized constituents may then bereacted with another element to change the properties and structure ofthe vaporized constituent elements.

Next, the vaporized and reacted constituent elements (which may bediamond) may be diffused into the surface of the substrate. A separatefabricated coating may be produced on the surface of the substratehaving the same or a different chemical composition than that of thevaporized and reacted constituent elements. Alternatively, some of thechanged constituent elements which were diffused into the substrate maybe vaporized and reacted again and deposited as a coating on the. Bythis process and variations of it, appropriate coatings such as diamond,cubic boron nitride, diamond like carbon, B₄C, SiC, TiC, TiN, TiB, cCN,Cr₃C₂, and Si₃N₄ may be formed on a substrate.

In other manufacturing environments, high temperature laser application,electroplating, sputtering, energetic laser excited plasma deposition orother methods may be used to place a volume of diamond, diamond-likematerial, a hard material or a superhard material in a location in whichwill serve as a bearing surface.

In light of the disclosure herein, those of ordinary skill in the artwill comprehend the apparatuses, materials and process conditionsnecessary for the formation and use of high quality diamond on asubstrate using any of the manufacturing methods described herein inorder to create a diamond bearing surface.

F. Manufacturing the Diamond Portion of Preferred Structures

This section provides information related to manufacturing the preferredprosthetic hip joint and other structures having similar geometry.

1. The Nature of the Problem

In areas outside of prosthetic joints, in particular in the field ofrock drilling cutters, polycrystalline diamond compacts have been usedfor some time. Historically those cutters have been cylindrical in shapewith a planar diamond table at one end. The diamond surface of a cutteris much smaller than the bearing surface needed in most prostheticjoints. Thus, polycrystalline diamond cutter geometry and manufacturingmethods are not directly applicable to prosthetic joints.

The particular problem posed by the manufacture of a prosthetic hipjoint is how to produce a concave spherical polycrystalline diamondcompact acetabular cup and a matching convex spherical polycrystallinediamond compact femoral head. In the manufacture of a sphericalpolycrystalline diamond compact, symmetry becomes a dominantconsideration in performing loading, sealing, and pressing/sinteringprocedures. The spherical component design requires that pressures beapplied radially in making the part. During the high pressure sinteringprocess, described in detail below, all displacements must be along aradian emanating from the center of the sphere that will be produced inorder to achieve the spherical geometry. To achieve this in hightemperature/high pressure pressing, an isostatic pressure field must becreated. During the manufacture of such spherical parts, if there is anydeviatoric stress component, it will result in distortion of the partand may render the manufactured part useless.

Special considerations that must be taken into account in makingspherical polycrystalline diamond compacts are discussed below.

a. Modulus

Most polycrystalline diamond compacts include both a diamond table and asubstrate. The material properties of the diamond and the substrate maybe compatible, but the high pressure and high temperature sinteringprocess in the formation of a polycrystalline diamond compact may resultin a component with excessively high residual stresses. For example, fora polycrystalline diamond compact using tungsten carbide as thesubstrate, the sintered diamond has a Young's modulus of approximately120 million p.s.i., and cobalt cemented tungsten carbide has a modulusof approximately 90 million p.s.i. Modulus refers to the slope of thecurve of the stress plotted against the stress for a material. Modulusindicates the stiffness of the material. Bulk modulus refers to theratio of isostatic strain to isostatic stress, or the unit volumereduction of a material versus the applied pressure or stress.

Because diamond and most substrate materials have such a high modulus, avery small stress or displacement of the polycrystalline diamond compactcan induce very large stresses. If the stresses exceed the yieldstrength of either the diamond or the substrate, the component willfail. The strongest polycrystalline diamond compact is not necessarilystress free. In a polycrystalline diamond compact with optimaldistribution of residual stress, more energy is required to induce afracture than in a stress free component. Thus, the difference inmodulus between the substrate and the diamond must be noted and used todesign a component that will have the best strength for its applicationwith sufficient abrasion resistance and fracture toughness.

b. Coefficient of Thermal Expansion

The extent to which diamond and its substrate differ in how they deformrelative to changes in temperature also affects their mechanicalcompatibility. Coefficient of thermal expansion (“CTE”) is a measure ofthe unit change of a dimension with unit change in temperature or thepropensity of a material to expand under heat or to contract whencooled. As a material experiences a phase change, calculations based onCTE in the initial phase will not be applicable. It is notable that whencompacts of materials with different CTE's and moduluses are used, theywill stress differently at the same stress.

Polycrystalline diamond has a coefficient of thermal expansion (as aboveand hereafter referred to as “CTE”) on the order of 2-4 micro inches perinch (10⁻⁶ inches) of material per degree (μin/in° C.). In contrast,carbide has a CTE on the order of 6-8 μin/in° C. Although these valuesappear to be close numerically, the influence of the high moduluscreates very high residual stress fields when a temperature gradient ofa few hundred degrees is imposed upon the combination of substrate anddiamond. The difference in coefficient of thermal expansion is less of aproblem in prior art cylindrical polycrystalline diamond compacts with aplanar diamond table than in the manufacture of spherical components orcomponents with other complex geometries for prosthetic joints. When aspherical polycrystalline diamond compact is manufactured, differencesin the CTE between the diamond and the substrate can cause high residualstress with subsequent cracking and failure of the diamond table, thesubstrate or both at any time during or after high pressure/hightemperature sintering.

C. Dilatoric and Deviatoric Stresses

The diamond and substrate assembly will experience a reduction of freevolume during the sintering process. The sintering process, described indetail below, involves subjecting the substrate and diamond assembly topressure ordinarily in the range of about 40 to about 68 kilobar. Thepressure will cause volume reduction of the substrate. Some geometricaldistortion of the diamond and/or the substrate may also occur. Thestress that causes geometrical distortion is called deviatoric stress,and the stress that causes a change in volume is called dilatoricstress. In an isostatic system, the deviatoric stresses sum to zero andonly the dilatoric stress component remains. Failure to consider all ofthese stress factors in designing and sintering a polycrystallinediamond component with complex geometry (such as concave and convexspherical polycrystalline diamond compacts) will likely result infailure of the process.

d. Free Volume Reduction of Diamond Feedstock

As a consequence of the physical nature of the feedstock diamond, largeamounts of free volume are present unless special preparation of thefeedstock is undertaken prior to sintering. It is necessary to eliminateas much of the free volume in the diamond as possible, and if the freevolume present in the diamond feedstock is too great, then sintering maynot occur. It is also possible to eliminate the free volume duringsintering if a press with sufficient ram displacement is employed. Isimportant to maintain a desired uniform geometry of the diamond andsubstrate during any process which reduces free volume in the feedstock,or a distorted or faulty component may result.

e. Selection of Solvent-Catalyst Metal

Formation of synthetic diamond in a high temperature and high pressurepress without the use of a solvent-catalyst metal is not a viable methodat this time. A solvent-catalyst metal is required to achieve desiredcrystal formation in synthetic diamond. The solvent-catalyst metal firstsolvates carbon preferentially from the sharp contact points of thediamond feedstock crystals. It then recrystallizes the carbon as diamondin the interstices of the diamond matrix with diamond-diamond bondingsufficient to achieve a solid with 95 to 97% of theoretical density withsolvent metal 5-3% by volume. That solid distributed over the substratesurface is referred to herein as a polycrystalline diamond table. Thesolvent-catalyst metal also enhances the formation of chemical bondswith substrate atoms.

When the polycrystalline diamond compact to be manufactured is intendedfor use in a biomedical application, it is essential to select a solventmetal which will be biocompatible. Prior art solvent-catalyst metals forpolycrystalline diamond compact formation are not biocompatible, so newsolvent metals which will perform satisfactorily and which arebiocompatible must be found.

A preferred method for adding the solvent-catalyst metal to diamondfeedstock is by causing it to sweep from the substrate that containssolvent-catalyst metal during high pressure and high temperaturesintering. Powdered solvent-catalyst metal may also be added to thediamond feedstock before sintering, particularly if thicker diamondtables are desired. An attritor method may also be used to add thesolvent-catalyst metal to diamond feedstock before sintering. If toomuch or too little solvent-catalyst metal is used, then the resultingpart may lack the desired mechanical properties, so it is important toselect an amount of solvent-catalyst metal and a method for adding it todiamond feedstock that is appropriate for the particular part to bemanufactured.

f. Diamond Feedstock Particle Size and Distribution

The wear characteristics of the finished diamond product are integrallylinked to the size of the feedstock diamond and also to the particledistribution. Selection of the proper size(s) of diamond feedstock andparticle distribution depends upon the service requirement of thespecimen and also its working environment. The wear resistance ofpolycrystalline diamond is enhanced if smaller diamond feedstockcrystals are used and a highly diamond-diamond bonded diamond table isachieved.

Although polycrystalline diamond may be made from single modal diamondfeedstock, use of multi-modal feedstock increases both impact strengthand wear resistance. The use of a combination of large crystal sizes andsmall crystal sizes of diamond feedstock together provides a part withhigh impact strength and wear resistance, in part because theinterstitial spaces between the large diamond crystals may be filledwith small diamond crystals. During sintering, the small crystals willsolvate and reprecipitate in a manner that binds all of the diamondcrystals into a strong and tightly bonded compact.

g. Diamond Feedstock Loading Methodology

Contamination of the diamond feedstock before or during loading willcause failure of the sintering process. Great care must be taken toensure the cleanliness of diamond feedstock and any addedsolvent-catalyst metal or binder before sintering.

In order to prepare for sintering, clean diamond feedstock, substrate,and container components are prepared for loading. The diamond feedstockand the substrate are placed into a refractory metal container called a“can” which will seal its contents from outside contamination. Thediamond feedstock and the substrate will remain in the can whileundergoing high pressure and high temperature sintering in order to forma polycrystalline diamond compact. The can will preferably be sealed byelectron beam welding at high temperature and in a vacuum.

Enough diamond aggregate (powder or grit) is loaded to account forlinear shrinkage during high pressure and high temperature sintering.The method used for loading diamond feedstock into a can for sinteringaffects the general shape and tolerances of the final part. Inparticular, the packing density of the feedstock diamond throughout thecan should be as uniform as possible in order to produce a good qualitysintered polycrystalline diamond compact structure. In loading, bridgingof diamond can be avoided by staged addition and packing.

The degree of uniformity in the density of the feedstock material afterloading will affect geometry of the polycrystalline diamond compact.Loading of the feedstock diamond in a dry form versus loading diamondcombined with a binder and the subsequent process applied for theremoval of the binder will also affect the characteristics of thefinished polycrystalline diamond compact. In order to properlypre-compact diamond for sintering, the pre-compaction pressures shouldbe applied under isostatic conditions.

h. Selection of Substrate Material

The unique material properties of diamond and its relative differencesin modulus and CTE compared to most potential substrate materialsdiamond make selection of an appropriate polycrystalline diamondsubstrate a formidable task. When the additional constraints ofbiocompatibility is placed on the substrate, the choice is even moredifficult. Most biocompatible metals are not compatible with thematerial properties of synthetic diamond. A great disparity in materialproperties between the diamond and the substrate creates challengessuccessful manufacture of a polycrystalline diamond component with theneeded strength and durability. Even very hard substrates appear to besoft compared to polycrystalline diamond. The substrate and the diamondmust be able to withstand not only the pressure and temperature ofsintering, but must be able to return to room temperature andatmospheric pressure without delaminating, cracking or otherwisefailing. Further, even among those materials that are believed to bebiocompatible, it is expedient to use only those which meet governmentalregulatory guidelines for products such as prosthetic joints.

Selection of substrate material also requires consideration of theintended application for the part, impact resistance and strengthsrequired, and the amount of solvent-catalyst metal that will beincorporated into the diamond table during sintering. Substratematerials must be selected with material properties that are compatiblewith those of the diamond table to be formed.

1. Substrate Geometry

In the invention, it is preferred to manufacture spherical,hemispherical, partially spherical, arcuate and other complex concaveand convex geometries of polycrystalline diamond compacts, which maylater be cut, machined and otherwise finished to serve as femoral heads,acetabular cups, other joint surfaces, other bearing surfaces, and otherwear-resistant surfaces. Formation of such parts requires considerationof the unique geometry of the substrate. In particular, the sphericalgeometry of the desired finished product requires that forces applied tothe substrate and diamond feedstock during sintering be along a radianemanating from the center of the sphere to be produced.

Further, it is important to consider whether to use a substrate whichhas a smooth surface or a surface with topographical features. Substratesurfaces may be formed with a variety of topographical features so thatthe diamond table is fixed to the substrate with both a chemical bondand a mechanical grip. Use of topographical features on the substrateprovides a greater surface area for chemical bonds and with themechanical grip provided by the topographical features, can result in astronger and more durable component.

2. Preferred Materials and Manufacturing Processes

The inventors have discovered and determined materials and manufacturingprocesses for constructing the preferred polycrystalline diamondcompacts for use in a prosthetic joint. These materials and methods willhave application outside of the field of prosthetics as well. It is alsopossible to manufacture the invented bearing surfaces by methods andusing materials other than those listed below.

The steps described below, such as selection of substrate material andgeometry, selection of diamond feedstock, loading and sintering methods,will affect each other, so although they are listed as separate stepsthat must be taken to manufacture a polycrystalline diamond compact, nostep is completely independent of the others, and all steps must bestandardized to ensure success of the manufacturing process.

a. Select Substrate Material

In order to manufacture any polycrystalline diamond component, anappropriate substrate should be selected. For the manufacture of apolycrystalline diamond component to be used in a prosthetic joint, theinventors prefer use of the substrates listed in the table below.

TABLE 2 SOME SUBSTRATES FOR BIOMEDICAL APPLICATIONS SUBSTRATE ALLOY NAMEREMARKS Titanium Ti6/4 (TiAlVa) A thin tantalum barrier is ASTM F-1313(TiNbZr) preferably placed on the ASTM F-620 titanium substrate beforeASTM F-1580 loading diamond feedstock. TiMbHf Approved biocompatibleNitinol (TiNi + other) material. Cobalt chrome ASTM F-799 Containscobalt, chromium and molybdenum. Wrought product. Approved biocompatiblematerial. Cobalt chrome ASTM F-90 Contains cobalt, chromium, tungstenand nickel. Approved biocompatible material. Cobalt chrome ASTM F-75Contains cobalt, chromium and molybdenum. Cast product. Approvedbiocompatible material. Cobalt chrome ASTM F-562 Contains cobalt,chromium, molybdenum and nickel. Approved biocompatible material. Cobaltchrome ASTM F-563 Contains cobalt, chromium, molybdenum, tungsten, ironand nickel. Approved biocompatible meterail. refractory metal. TantalumASTM F-560 (unalloyed) Approved biocompatible Platinum various NiobiumASTM F-67 (unalloyed) Approved biocompatible refracto metal. MaganeseVarious May include Cr, Ni, Mg, molybdenum. Cobalt cemented WC Notapproved in the U.S. tungsten carbide for prosthetic applications at thetime of writing. Cobalt chrome CoCr cemented WC CoCr is an approvedcemented biocompatible material. tungsten carbide Cobalt chrome CoCrcemented CrC CoCr is an approved cemented chrome biocompatible material.carbide Cobalt chrome CoCr cemented SiC CoCr is an approved cementedsilicon biocompatible material. carbide Fused silicon SiC carbide Cobaltchrome CoCrMo A thin tungsten or molybdenum tungsten/cobalt layer isplaced on the substrate before loading diamond feedstock. Stainlesssteel Various Approved biocompatible material.

The CoCr used is preferably either CoCrMo or CoCrW. The precedingsubstrates are examples only. In addition to these substrates, othermaterials may be appropriate for use as substrates for construction ofprosthetic joints and other bearing surfaces.

When titanium is used as the substrate, it is sometimes preferred by theinventors to place a thin tantalum barrier layer on the titaniumsubstrate. The tantalum barrier prevents mixing of the titanium alloyswith cobalt alloys used in the diamond feedstock. If the titanium alloysand the cobalt alloys mix, it possible that a detrimentally low meltingpoint eutectic inter-metallic compound will be formed during the highpressure and high temperature sintering process. The tantalum barrierbonds to both the titanium and cobalt alloys, and to the polycrystallinediamond that contains cobalt solvent-catalyst metals. Thus, apolycrystalline diamond compact made using a titanium substrate with atantalum barrier layer and diamond feedstock that has cobaltsolvent-catalyst metals can be very strong and well formed.Alternatively, the titanium substrate may be provided with an alpha caseoxide coating (an oxidation layer) forming a barrier which preventsformation of a eutectic metal.

If a cobalt chrome molybdenum substrate is used, it is preferred toplace either a thin tungsten layer or a thin tungsten and cobalt layeron the substrate before loading of the diamond feedstock in order tocontrol formation of chrome carbide (CrC) during sintering.

In addition to those listed, other appropriate substrates may be usedfor forming polycrystalline diamond compact bearing surfaces. Further,it is possible within the scope of the invention to form a diamondbearing surface for use without a substrate. It is also possible to forma bearing surface from any of the superhard materials and other bearingmaterials listed herein, in which case a substrate may not be needed.Additionally, if it is desired to use a type of diamond or carbon otherthan polycrystalline diamond, substrate selection may differ. Forexample, if a diamond bearing surface is to be created by use ofchemical vapor deposition or physical vapor deposition, then use of asubstrate appropriate for those manufacturing environments and for thecompositions used will be necessary.

b. Determination of Substrate Geometry

1.) General Substrate Configuration

A substrate geometry appropriate for the compact to be manufactured andappropriate for the materials being used should be selected. In order tomanufacture a concave spherical acetabular cup or a convex sphericalfemoral head as preferred in some embodiments of the invention, it isnecessary to select a substrate geometry that will facilitate themanufacture of those parts. In order to ensure proper diamond formationand avoid compact distortion, forces acting on the diamond and thesubstrate during sintering must be strictly radial. Therefore thepreferred substrate geometry at the contact surface with diamondfeedstock for manufacturing an acetabular cup, a femoral head, or anyother spherical component is generally spherical.

As mentioned previously, there is a great disparity in the materialcharacteristics of synthetic diamond and most available substratematerials. In particular, modulus and CTE are of concern. But whenapplied in combination with each other, some substrates can form astable and strong spherical polycrystalline diamond compact. The tablebelow lists physical properties of some preferred substrate materials.

TABLE 3 MATERIAL PROPERTIES OF SOME PREFERRED SUBSTRATES SUBSTRATEMATERIAL MODULUS CTE Ti 6/4 16.5 million psi 5.4 CoCrMo 35.5 million psi16.9 CoCrW 35.3 million psi 16.3

Use of either titanium or cobalt chrome substrates alone for themanufacture of spherical polycrystalline diamond compacts may result incracking of the diamond table or separation of the substrate from thediamond table. In particular, it appears that titanium's dominantproperty during high pressure and high temperature sintering iscompressibility while cobalt chrome's dominant property during sinteringis CTE. In some embodiments of the invention, a substrate of two or morelayers may be used in order to achieve dimensional stability during andafter manufacturing.

Referring to the table below, some combinations of substrate materialsthat may be used for making spherical polycrystalline diamond compactsare listed.

TABLE 4 SPHERICAL SUBSTRATE COMBINATIONS for Making Convex PCD SpheresSUBSTRATE CORE SUBSTRATE SHELL REMARKS Ti 6/4 ASTM F-136 sphere CoCrASTM F-799 Alpha case oxide coating on titanium or tantalum barrierlayer on titanium. Ti 6/4 ASTM F-136 sphere CoCr ASTM F-90 Alpha caseoxide coating on titanium or tantalum barrier layer on titanium. CoCrASTM F-799 sphere Ti 6/4 ASTM F-136 Tantalum barrier layer on titanium.CoCr ASTM F-90 sphere Ti 6/4 ASTM F-136 Tantalum barrier layer ontitanium. CoCr ASTM F-799 sphere None Substrate surface topographicalfeatures used, as described below. Al₂O₃ ceramic core sphere None

The alpha case oxide coating is used to seal the titanium from reactingwith the cobalt chrome. The tantalum barrier layer can be in the rangeof about 0.002 to 0.010 inches thick with 0.008 believed to be optimal.

A two piece substrate as mentioned above may be used to achievedimensional stability in spherical parts. A two piece substrate mayovercome differences in CTE and modulus between diamond and thesubstrate. It appears that use of a substrate with a plurality of layersovercomes the tendencies of the materials to expand and contract atdifferent rates, which if not addressed will cause cracking of thediamond.

A spherical substrate having at least two distinct layers of differentsubstrate materials can be employed to stabilize the component andprevent the substrate from shrinking away from the diamond table, thusresulting in the successful manufacture of spherical polycrystallinediamond compacts.

Referring to FIGS. 5A-5F, various substrate structures of the inventionfor making a generally spherical polycrystalline diamond compact aredepicted. FIGS. 5A and 5B depict two-layer substrates.

In FIG. 5A, a solid first sphere 501 of a substrate material intended tobe used as the substrate shell or outer layer was obtained. Thedimensions of the first sphere 501 are such that the dimension of thefirst sphere 501 with a diamond table on its exterior will approximatethe intended dimension of the component prior to final finishing. Oncethe first sphere 501 of the substrate is obtained, a hole 502 is boredinto its center. The hole 502 is preferably bored, drilled, cut, blastedor otherwise formed so that the terminus 503 of the hole 502 ishemispherical. This is preferably achieved by using a drill bit or endmill with a round or ball end having the desired radius and curvature.

Then a second sphere 504 of a substrate material is obtained. The secondsphere 504 is smaller than the first sphere 501 and is be placed in hole502 in the first sphere 501. The substrates materials of spheres 501 and504 are preferably selected form those listed in the tables above. Theymay also be of other appropriate materials. The second sphere 504 andthe hole 502 and its terminus 503 should fit together closely withoutexcessive tolerance or gap.

A plug 505 preferably of the same substrate material as first sphere 501is formed or obtained. The plug 505 has a first end 505 a and a secondend 505 b and substrate material therebetween in order to fill the hole502 except for that portion of the hole 502 occupied by the secondsphere 504 adjacent the hole terminus 503. The plug 505 preferably has aconcave hemispherical receptacle 506 at its first end 505 a so that plug505 will closely abut second sphere 504 across about half the sphericalsurface of second sphere 504. The plug 505 is generally cylindrical inshape. The substrate assembly including one substrate sphere placedinside of another may then be loaded with diamond feedstock 507 andsintered under high pressure at high temperature to form a sphericalpolycrystalline diamond compact.

Referring to FIG. 5B, another substrate geometry for manufacturingspherical polycrystalline diamond compacts of the invention is depicted.An inner core sphere 550 of appropriate substrate material is selected.Then an outer substrate first hemisphere 551 and outer substrate secondhemisphere 552 are selected. Each of the outer substrate first andsecond hemispheres 551 and 552 are formed so that they each have ahemispherical receptacle 551 a and 552 a shaped and sized to accommodateplacement of the hemispheres about the exterior of the inner core sphere550 and thereby enclose and encapsulate the inner core sphere 550. Thesubstrates materials of inner core sphere 550 and hemispheres 551 and552 are preferably selected form those listed in the tables above orother appropriate materials.

With the hemispheres and inner core sphere assembled, diamond feedstock553 may be loaded about the exterior of the hemispheres and hightemperature and high pressure sintering may proceed in order to form aspherical polycrystalline diamond compact.

Although FIGS. 5A and 5B depict two-layer substrates, it is possible touse multiple layer substrates (3 or more layers) for the manufacture ofpolycrystalline diamond compacts or polycrystalline cubic boron nitridecompacts. The selection of a substrate material, substrate geometry,substrate surface topographical features, and substrates having aplurality of layers (2 or more layers) of the same or differentmaterials depend at least in part on the thermo-mechanical properties ofthe substrate, the baro-mechanical properties of the substrate, and thebaro-mechanical properties of the substrate.

Referring to FIG. 5C, another substrate configuration for makinggenerally spherical polycrystalline diamond compacts is depicted. Thesubstrate 520 is in the general form of a sphere. The surface of thesphere includes substrate surface topography intended to enhancefixation of a diamond table to the substrate. The substrate has aplurality of depressions 521 formed on its surface. Each depression 521is formed as three different levels of depression 521 a, 521 b and 521c. The depressions are depicted as being concentric circles, each ofapproximately the same depth, but their depths could vary, the circlesneed not be concentric, and the shape of the depressions need not becircular. The depression walls 521 d, 521 e and 521 f are depicted asbeing parallel to a radial axis of the depressions which axis is normalto a tangent to the theoretical spherical extremity of the sphere, butcould have a different orientation if desired. As depicted, the surfaceof the substrate sphere 522 has no topographical features other than thedepressions already mentioned, but could have protrusions, depressionsor other modifications as desired. The width and depth dimensions of thedepressions 521 may be varied according to the polycrystalline diamondcompact that is being manufactured.

Diamond feedstock may be loaded against the exterior of the substratesphere 520 and the combination may be sintered at diamond stablepressures to produce a spherical polycrystalline diamond compact. Use ofsubstrate surface topographical features on a generally sphericalsubstrate provides a superior bond between the diamond table and thesubstrate as described above and permits a polycrystalline diamondcompact to be manufactured using a single layer substrate. That isbecause of the gripping action between the substrate and the diamondtable achieved by use of substrate surface topographical features.

Referring to FIG. 5D, a segmented spherical substrate 523 is depicted.The substrate has a plurality of surface depressions 524 equally spacedabout its exterior surface. These depressions as depicted are formed inlevels of three different depths. The first level 524 a is formed to apredetermined depth and is of pentagonal shape about its outerperiphery. The second level 524 b is round in shape and is formed to apredetermined depth which may be different from the predetermined depthof the pentagon. The third level 524 c is round in shape in is formed toa predetermined depth which may be different from each of the otherdepths mentioned above. Alternatively, the depressions may be formed toonly one depth, may all be pentagonal, or may be a mixture of shapes.The depressions may be formed by machining the substrate sphere.

Referring to FIG. 5E, a cross section of an alternative substrateconfiguration for making a polycrystalline diamond compact is shown. Apolycrystalline diamond compact 525 is shown. The compact 525 isspherical. The compact 525 includes a diamond table 526 sintered to asubstrate 527. The substrate is partially spherical in shape at itsdistal side 527 a and is dome-shaped on its proximal side 527 b.Alternatively, the proximal side 527 b of the substrate 527 may bedescribed as being partially spherical, but the sphere on which it isbased has a radius of smaller dimension than the radius of the sphere onwhich the distal side 527 a of the substrate is based. Each of the top527 c and bottom 527 d are formed in a shape convenient to transitionfrom the proximal side 527 b substrate partial sphere to the distal side527 a substrate partial sphere. This substrate configuration hasadvantages in that it leaves a portion of substrate exposed for drillingand attaching fixation components without disturbing residual stressfields of the polycrystalline diamond table. It also provides a portionof the substrate that does not have diamond sintered to it, allowingdilatation of the substrate during sintering without disruption of thediamond table. More than 180 degrees of the exterior of the substratesphere has diamond on it, however, so the part is useful as a femoralhead or other articulation surface.

Referring to FIG. 5F, a cross section of an alternative substrateconfiguration for making a polycrystalline diamond compact is shown. Apolycrystalline diamond compact 528 is depicted having a diamond table529 and a substrate 530. The substrate has topographical features 531for enhancing strength of the diamond to substrate interface. Thetopographical features may include rectangular protrusions 532 spacedapart by depressions 533 or corridors. The distal side of the substrateis formed based on a sphere of radius r. The proximal side of thesubstrate 530 b is formed based on a sphere of radius r′, where r>r′.Usually the surface modifications will be found beneath substantiallyall of the diamond table.

Referring to FIG. 5G, a femoral head 535 of a prosthetic hip joint isdepicted. The femoral head 535 that includes a diamond table 536sintered to a substrate 536. The substrate is configured as a spherewith a protruding cylindrical shape. The head 535 is formed so that aquantity of substrate protrudes from the spherical shape of the head toform a neck 538 which may be attached to an appropriate body by anyknown attachment method, such as by self-locking taper fit, welding,threads or other attachment mechanisms. The use of a neck 538 preformedon the substrate that is used to manufacture a polycrystalline diamondcompact 535 provides an attachment point on the polycrystalline diamondcompact that may be utilized without disturbing the residual stressfield of the compact. The neck 538 depicted is an integral component ofa stem 540.

Any of the previously mentioned substrate configurations and substratetopographies and variations and derivatives of them may be used tomanufacture a polycrystalline diamond compact for use in a prosthetic orother load bearing or articulation surface environment.

In various embodiments of the invention, a single layer substrate may beutilized. In other embodiments of the invention, a two-layer substratemay be utilized, as discussed. Depending on the properties of thecomponents being used, however, it may be desired to utilize a substratethat includes three, four or more layers. Such multi-layer substratesare intended to be comprehended within the scope of the invention.

The preferred substrate geometry for manufacturing an acetabular cup orother concave spherical, hemispherical or partially sphericalpolycrystalline diamond compact of the invention differs from that usedto manufacture a convex spherical polycrystalline diamond compact.Referring to FIGS. 6A-6C below, the preferred substrate geometry andassembly for manufacturing a concave spherical polycrystalline diamondcompact (such as that used in an acetabular cup) are depicted. Thesubstrate 601 (and 601 a and 601 b) is preferably in the form of acylinder with a hemispherical receptacle 602 (and 602 a and 602 b)formed into one of its ends.

Two substrate cylinders 601 a and 601 b are placed so that theirhemispherical receptacles 602 a and 602 b are adjacent each other, thusforming a spherical cavity 604 between them. A sphere 603 of anappropriate substrate material is located in the cavity 604. Diamondfeedstock 605 is located in the cavity 604 between the exterior of thesphere 603 and the concave surfaces of the receptacles 602 a and 602 bof the substrate cylinders 601 a and 601 b. The assembly is placed intoa refractory metal can 610 for sintering. The can has a first cylinder610 a and a second cylinder 601 b. The two cylinders join at a lip 611.

After such an assembly is sintered, the assembly may be slit, cut orground along the center line 606 in order to form a first cup assembly607 a and a second cup assembly 607 b. The preferred substrate materialsfor the cylinders 602 a and 602 b are CoCrMo (ASTM F-799) and CoCrW(ASTM F-90), and the preferred substrate material for the sphere 603 ispreferably CoCrMo (ASTM F-799), although any appropriate substratematerial may be used, including some of those listed in the tables.

While two layer substrates have been discussed above for manufacturingconcave and convex spherical polycrystalline diamond compacts, it isalso possible to use substrates consisting of more than two layers ofmaterial or substrates of a single type of material in manufacturingspherical polycrystalline diamond compacts.

2.) Substrate Surface Topography

Depending on the application, it may be advantageous to includesubstrate surface topographical features on a substrate that is to beformed into a polycrystalline diamond compact. Regardless whether aone-piece, a two-piece of a multi-piece substrate is used, it may bedesirable to modify the surface of the substrate or providetopographical features on the substrate in order to increase the totalsurface area of diamond to enhance substrate to diamond contact and toprovide a mechanical grip of the diamond table.

The placement of topographical features on a substrate serves to modifythe substrate surface geometry or contours from what the substratesurface geometry or contours would be if formed as a simple planar ornon-planar figure. Substrate surface topographical features may includeone or more different types of topographical features which result inprotruding, indented or contoured features that serve to increasesurface, mechanically interlock the diamond table to the substrate,prevent crack formation, or prevent crack propagation.

Substrate surface topographical features or substrate surfacemodifications serve a variety of useful functions. Use of substratetopographical features increases total substrate surface area of contactbetween the substrate and the diamond table. This increased surface areaof contact between diamond table and substrate results in a greatertotal number of chemical bonds between diamond table and substrate thanif the substrate surface topographical features were absent, thusachieving a stronger polycrystalline diamond compact.

Substrate surface topographical features also serve to create amechanical interlock between the substrate and the diamond table. Themechanical interlock is achieved by the nature of the substratetopographical features and also enhances strength of the polycrystallinediamond compact.

Substrate surface topographical features may also be used to distributethe residual stress field of the polycrystalline diamond compact over alarger surface area and over a larger volume of diamond and substratematerial. This greater distribution can be used to keep stresses belowthe threshold for crack initiation and/or crack propagation at thediamond table/substrate interface, within the diamond itself and withinthe substrate itself.

Substrate surface topographical features increase the depth of thegradient interface or transition zone between diamond table andsubstrate, in order to distribute the residual stress field through alonger segment of the composite compact structure and to achieve astronger part.

Substrate surface modifications can be used to created a sinteredpolycrystalline diamond compact that has residual stresses that fortifythe strength of the diamond layer and yield a more robustpolycrystalline diamond compact with greater resistance to breakage thanif no surface topographical features were used. This is because in orderto break the diamond layer, it is necessary to first overcome theresidual stresses in the part and then overcome the strength of thediamond table.

Substrate surface topographical features redistribute forces received bythe diamond table. Substrate surface topographical features cause aforce transmitted through the diamond layer to be re-transmitted fromsingle force vector along multiple force vectors. This redistribution offorces travelling to the substrate avoids conditions that would deformthe substrate material at a more rapid rate than the diamond table, assuch differences in deformation can cause cracking and failure of thediamond table.

Substrate surface topographical features may be used to mitigate theintensity of the stress field between the diamond and the substrate inorder to achieve a stronger part.

Substrate surface topographical features may be used to distribute theresidual stress field throughout the polycrystalline diamond compactstructure in order to reduce the stress per unit volume of structure.

Substrate surface topographical features may be used to mechanicallyinterlock the diamond table to the substrate by causing the substrate tocompress over an edge of the diamond table during manufacturing.Dovetailed, hemispherical and lentate modifications act to provide forcevectors that tend to compress and enhance the interface of diamond tableand substrate during cooling as the substrate dilitates radially.

Substrate surface topographical features may also be used to achieve amanufacturable form. As mentioned herein, differences in coefficient ofthermal expansion and modulus between diamond and the chosen substratemay result in failure of the polycrystalline diamond compact duringmanufacturing. For certain parts, the stronger interface betweensubstrate and diamond table that may be achieved when substratetopographical features are used can achieve a polycrystalline diamondcompact that can be successfully manufactured. But if a similar part ofthe same dimensions is to be made using a substrate with a simplesubstrate surface rather than specialized substrate surfacetopographical features, the diamond table may crack or separate from thesubstrate due to differences in coefficient of thermal expansion ormodulus of the diamond and the substrate.

Examples of useful substrate surface topographical features includewaves, grooves, ridges, other longitudinal surface features (any ofwhich may be arranged longitudinally, lattitudinally, crossing eachother at a desired angle, in random patterns, and in geometricpatterns), three dimensional textures, spherical segment depressions,spherical segment protrusions, triangular depressions, triangularprotrusions, arcuate depressions, arcuate protrusions, partiallyspherical depressions, partially spherical protrusions, cylindricaldepressions, cylindrical protrusions, rectangular depressions,rectangular protrusions, depressions of n-sided polygonal shapes where nis an integer, protrusions of n-sided polygonal shapes, a waffle patternof ridges, a waffle iron pattern of protruding structures, dimples,nipples, protrusions, ribs, fenestrations, grooves, troughs or ridgesthat have a cross-sectional shape that is rounded, triangular, arcuate,square, polygonal, curved, or otherwise, or other shapes. Machining,pressing, extrusion, punching, injection molding and other manufacturingtechniques for creating such forms may be used to achieve desiredsubstrate topography. Although for illustration purposes, some sharpcomers are depicted on substrate topography or other structures in thedrawings, in practice it is expected that all comers will have a smallradius to achieve a component with superior durability.

FIGS. 3A-3U depict a few possible substrate surface modifications.Referring to FIG. 3A, a femoral head is depicted that features concaveand convex substrate surface topographical features. A femoral head 380is shown that has a diamond table 382 sintered to a substrate 383. Thesubstrate 383 has surface topography that includes concave arcuategrooves 384 and convex arcuate ridges 385 radiating from a point on thesubstrate. The diamond 382 covers the substrate topographical features,resulting in a greater surface area of contact between the diamond tableand the substrate than if a simple rounded substrate were employed.

FIG. 3B shows redistribution of a force applied to the femoral head 380of FIG. 3A. When a force F1 is applied to the head 380, that force F1 isredistributed along force vectors F2 and F3, as shown. Thus, although onthe diamond table 382 a single force vector is received, that forcevector is broken down into smaller forces and transmitted through thesubstrate 383. This redistribution of forces decreases the possibilityof a differential in rates of deformation of the diamond table and thesubstrate and therefore reduces the chance of the diamond table crackingand failing.

FIG. 3C depicts use of substrate topographical features on a femoralhead in a prosthetic joint. The acetabular cup 386 is mounted in thepelvic bone 387. The cup 386 has a polycrystalline diamond table 388attached to a substrate 389. The femoral head 390 includes a table ofpolycrystalline diamond 391 on a substrate 392.

The substrate 392 has surface topography including grooves 393 orientedso that they will be generally vertical when the joint is in standinguse in a patient. The primary force vector F1 is generally parallel tothe grooves 393 in a standing position. The force zone 394 due towalking is shown in bone above the cup. Use of substrate surfacetopography that includes grooves that are generally vertically orientedin a standing patient achieves wider redistribution of forces.

FIG. 3D depicts a convex sphere 350 of appropriate substrate material.The sphere 350 has a polar axis 351 and an equator 352. A plurality ofsurface modifications 353 were formed in the surface of the sphere 350.The surface modifications are arranged in a close offset configuration.The surface modifications can range from less than about 0.001 inch tomore than about 0.750 inch diameter cylindrical depressions having adepth of from less than about 0.001 inch to more than about 0.750 inchor otherwise as desired. Very small surface topographical features canbe created by use of a laser. In most embodiments of the invention,substrate surface topographical features will cover from about 1% toabout 99% of the surface of the substrate beneath the diamond table. Thesubstrate surface topographical features will have a depth of from about1% of the radius of the part to about 50% of the radius of the part.Discrete substrate surface topographical features will have a dimensionmeasured along a tangent to the substrate surface of from about 1% toabout 50% of the radius of the part.

FIG. 3E depicts a cross section of a polycrystalline diamond compactformed using a spherical substrate with a modified substrate surface,such as that depicted in FIG. 3A. The compact 360 has a diamond layer361 sintered to a substrate 362. The substrate 362 has surfacemodifications 363 in which diamond 361 is found. The substrate in thevicinity of the surface modification 363 tends to grip the diamond atforce lines F1 and F2, thus adding a mechanical gripping advantage tothe chemical bonds of the polycrystalline diamond compact, and resultingin a very strong part.

FIG. 3F depicts substrate surface convex rounded protrusions 379 ornipples on a substrate 378. The nipples or protrusions are depicted asbeing rounded or arcuate. FIG. 3G depicts substrate surface protrudingridges 377 and grooves 376 on a substrate 375. FIG. 3H depicts asubstrate 374 having elevated ridges 273 and rounded or arcuate grooves372 between the ridges. This substrate surface configuration may be madeby machining grooves that are round in cross section in a sphericalsubstrate. The ridges 377 are substrate material left between thegrooves that have been machined.

FIG. 3I depicts a convex spherical substrate 320. Absent specializedsubstrate surface topographical features, the substrate 320 would be inthe form of a simple sphere as depicted by circle 323. This substrate320 includes rounded or arcuate wavelike forms on its exterior surfacethat take the shape of protruding ridges 322 and depressed grooves 321.

FIG. 3J depicts a convex spherical substrate 324. The substrate 324includes protruding rectangular forms 325 which form a waffle-likepattern on the surface of the substrate 324. Between each protrudingform 325 is a gap, groove, trough, or alley 326.

FIG. 3K depicts a substrate 327. Such a substrate may have been simpleconvex spherical as indicated by dashed circle 328, but has beenmachined to have its present form. The substrate 327 has had polygonalshapes 329 formed into its surface to create specialized topographicalfeatures for an interface with a diamond table.

FIG. 3L depicts a generally spherical substrate 330 having a pluralityof depressions 331 formed in its surface. The surface 334 of thesubstrate sphere 330 is spherical in shape except for the depressions331. The depressions have a circular upper rim 335, a circular bottom332, and a sidewall 333 of a desired depth. As desired, the maximumdiameter of the rim 335 of a depression may have the same or greaterdimension than the maximum diameter of the bottom 332 of the samedepression. If the two diameters are the same, then the depression willhave a cylindrical shape. If the rim 335 has a greater diameter than thebottom 333, then the depression will have a frusto-conical shape.Diamond may be bonded on a substrate as depicted in FIG. 3L in tablethat has a thickness that completely covers the outside surface of thesubstrate. In that case, the diamond table will be thicker in areasabove a depression than in other areas. If such a diamond table is used,then from outward appearance, the substrate surface topographicalfeatures will not be discernible. Alternatively, diamond may be bondedin the depressions only, leaving the substrate between depressionsexposed. Such a configuration is discussed in more detail with respectto FIG. 3Q.

FIG. 3M depicts a generally spherical substrate 336 having a pluralityof protrusions 337 on its surface. The surface 338 of the substratesphere 336 is spherical in shape except for the protrusions 337. Theprotrusions have a circular lower rim 339, a circular upper rim 340, anda sidewall 341 of a desired height. The protrusion tops 342 may be ofany desired shape, such as flat, domed, partially spherical, arcuate, orotherwise. As desired, the maximum diameter of the lower rim 339 and theupper rim 340 may differ. If the two diameters are the same and thesidewall 341 is straight, then the protrusion will have a generallycylindrical shape. If the rim 339 has a greater diameter than the rim340, then the protrusion will have a generally frusto-conical shape. Adiamond table may be attached to the substrate of FIG. 3M to that thediamond table completely covers the substrate surface modifications andthe areas between them. In such a configuration, from outward appearancethe substrate surface modifications would not be discernible.Alternatively, diamond may be attached to the substrate only between thesubstrate surface modifications, creating a web or network of exposeddiamond having discontinuous areas of exposed substrate material.

FIG. 3N depicts a spherical polycrystalline diamond compact 342including a diamond table 343 and a substrate 344. The substrate 344includes topographical surface modifications. The surface modificationsinclude dovetail depressions 345 formed in the substrate.Polycrystalline diamond has formed in the dovetail to create a tightmechanical interlock between the diamond table and the substrate. Thisstructure may be achieved by forming depressions in the surface of asubstrate that do not have a dovetail shape. During sintering, thedovetail interlock between the substrate and the diamond table can beformed due to differences in the coefficient of thermal expansion andmodulus between diamond and the substrate material.

FIG. 3O depicts a partially spherical polycrystalline diamond compact345 having a diamond table 346 and a substrate 347. The diamond table346 presents a continuous diamond load bearing and articulation surface.The substrate 347 has been formed with surface topography intended toeffect a stronger bond with the diamond table. The substrate 347includes hemispherical or lentate modifications 348 formed on thesubstrate outer surface. The modifications depicted are concavepartially spherical depressions on the substrate surface.Polycrystalline diamond forms in the depressions 349. During sintering,as the polycrystalline diamond compact cools, the substrate tends todilatate radially. The hemispherical depressions of this surfacemodification provide force vectors that compress and enhance theinterface between the diamond table and the substrate, to achieve a muchstronger bond between the diamond table and the substrate. Thus, amechanical grip or interlock is created between the diamond table andthe substrate both as a result of the differences in CTE between thediamond and the substrate and as a result of the substrate topographicalfeatures.

FIG. 3P depicts a partially spherical polycrystalline diamond compact320. The compact 320 includes a diamond table 321 and a substrate 322.The substrate 322 has topographical features that include ridges 323 andtroughs 324 that are triangular in cross section. The use of substratetopographical features such as these provides a gradient interface ortransition zone between the diamond and the substrate as describedelsewhere herein. The gradient interface I found in a polycrystallinediamond compact that has substrate topographical features is typicallyof greater depth than that found in a polycrystalline diamond compactthat has a substrate with a simple surface. Consequently, the residualstress field in a polycrystalline diamond compact that has substratetopographical features is distributed through a longer segment of thecomposite compact structure, and is distributed over a greater volume ofdiamond and substrate materials. The result is a polycrystalline diamondcompact that is stronger and more stable than that which may be achievedwithout the use of substrate topographical features.

FIG. 3Q depicts a partially spherical polycrystalline diamond compact.The compact includes a substrate 348 formed with diamond receptacles,depressions or indentations 351. On sintering, polycrystalline diamond349 is formed in the depressions 351 in order to create a load bearingand articulation surface that includes discontinuous or segmented areasof diamond. Between the diamond areas 349, there is exposed substratematerial 350 on the load bearing and articulation surface. During finishpolishing, the lesser hardness of the substrate material compared todiamond will tend to cause the exposed substrate 350 to be relieved,presenting a load bearing and articulation surface on which the primarycontact and articulation is provided by the diamond patches 349. Ifdesired, the exposed substrate 350 may be machined or polished toprovide sufficient relief to serve as a channel for communicatinglubricating fluids to the load bearing and articulation surface.

FIG. 3R depicts a spherical ball 352 that has a substrate 353 and adiamond table 354. The substrate 353 includes a receptacle 355 forreceiving an attachment mechanism. The diamond table 354 covers lessthan the entire surface of the substrate 353. As depicted, the diamondtable 354 has a hemispherical configuration. The substrate 353 has beenprepared with an annular groove or ring 356 about its equator. Thediamond table 354 is thicker in the area of the annular groove 356 andoccupies the annular groove 356 in order to provide strong bonding atthe edge of the diamond table 354.

FIG. 3S depicts a cup 357 having a substrate 358 and a diamond tableload bearing and articulation surface 359. The substrate 358 includes alip 360 which interlocks the diamond table 359 in place in the cup 357.Although the lip 360 structure may be formed in the substrate 358 priorto sintering of the polycrystalline diamond compact, the lip 360structure may also be formed or enhanced by dilatation of the substratematerial during sintering. The lip reduces or eliminates edge effect atthe extreme radial interface of the diamond table 359 and the substrate358 in order to provide a stronger and more durable component.

FIG. 3T depicts a generally spherical substrate 362 having a pluralityof truncated pyramid-like or polygonal protrusions 363 on its surface.The surface 364 of the substrate sphere 362 is generally spherical inshape except for the protrusions 363. The protrusions have a square orrectangular lower perimeter 365, a square or rectangular upper perimeter366 and a side wall 37 of desired height. The protrusion tops 366 maydiffer to form a plurality of different angles between the lower andupper perimeters. If the two perimeters are the same dimension and thesidewall 367 is straight, then the protrusions will have a generallysquare or rectangular shape. If the upper perimeter 366 has a smallerdimension than the lower perimeter, then the protrusion will have agenerally truncated pyramid shape. If the upper perimeter 366 is largerthan the lower perimeter 365, the protrusion will have a generallyinverted truncated pyramid shape. A diamond table may attach to thesubstrate of FIG. 3T so that the diamond table completely covers thesubstrate surface modifications and the areas between them. In such aconfiguration, from outward appearance, the substrate surfacemodifications would not be discernable. Alternatively, diamond may beattached to the substrate only between the substrate surfacemodifications, creating a web or network of exposed diamond havingdiscontinuous areas of exposed substrate material.

FIG. 3U depicts a generally spherical substrate 368 having a pluralityof depressions 369 formed into its surface. The surface 370 of thesubstrate sphere 368 is spherical in shape except for the depressions369. The depressions have a square or rectangular upper perimeter 37, asquare or rectangular bottom 372, and a sidewall 373 of a desired depth.As desired, the maximum upper perimeter 371 of a depression may have thesame dimension of the bottom perimeter 372 of the same depression. Ifthe perimeters are the same, then the depression will have a rectangularsquare shape. If the upper perimeter 371 has a greater dimension thanthe bottom perimeter 352, then the depression will have an invertedtruncated pyramid shape. Diamond may be bonded on a substrate asdepicted in FIG. 3U in a table that has a thickness that completelycovers the outside surface of the substrate. In that case the diamondtable will be thicker in areas above a depression than in other areas.If such a diamond table is used, then from outward appearance, thesubstrate surface topographical features will not be discernible.Alternatively, diamond may be bonded in the depressions only, leavingthe substrate between depressions exposed.

Although many substrate topographies have been depicted in convexspherical substrates, those surface topographies may be applied toconvex spherical substrate surfaces, other non-planar substratesurfaces, and flat substrate surfaces. Substrate surface topographieswhich are variations or modifications of those shown, and othersubstrate topographies which increase component strength or durabilitymay also be used.

C. Diamond Feedstock Selection

It is anticipated that typically the diamond particles used will be inthe range of less than 1 micron to more than 100 microns. In someembodiments of the invention, however, diamond particles as small as 1nanometer may be used. Smaller diamond particles are preferred forsmoother bearing surfaces. Commonly, diamond particle sizes will be inthe range of 0.5 to 2.0 microns or 0.1 to 10 microns.

A preferred diamond feedstock is shown in the table below.

TABLE 3 EXAMPLE BIMODAL DIAMOND FEEDSTOCK MATERIAL AMOUNT 4 to 8 microndiamond about 90% 0.5 to 1.0 micron diamond about 9% Titaniumcarbonitride powder about 1%

This formulation mixes some smller and some larger diamond crystals sothat during sintering, the small crystals may dissolve and thenrecrystallize in order to form a lattice structrure with the largerdiamond crystals. Titanium carbonitride powder may optionally be incudedin the diamond feedstick in order to prevent excessive diamond graingrowth during sintering in order to produce a finished product that hassmaller diamond crystals.

Another diamond feedstick example is provided in the table below.

TABLE 4 EXAMPLE TRIIMODAL DIAMOND FEEDSTOCK MATERIAL AMOUNT Size xdiamond crystals about 90% Size 0.1x diamond crystals about 9% Size0.01x diamond crystals about 1%

The trimodal diamond feedstock described above can be used with anysuitable diamond feedstock having a first size or diameter “x”, a secondsize 0.1x and a third size 0.01x. This ratio of diamond crystals allowspacking of the feedstock to about 89% theoretical density, closing mostinterstitial spaces and providing the densest diamond table in thefinished polycrystalline diamond compact.

Another diamond feedstock example is provided in the table below.

TABLE 5 EXAMPLE TRIIMODAL DIAMOND FEEDSTOCK MATERIAL AMOUNT Size xdiamond crystals about 88-92% Size 0.1x diamond crystals about 8-12%Size 0.01x diamond crystals about 0.8-1.2%

Another diamond feedstock example is provided in the table below.

TABLE 6 EXAMPLE TRIIMODAL DIAMOND FEEDSTOCK MATERIAL AMOUNT Size xdiamond crystals about 85-95% Size 0.1x diamond crystals about 5-15%Size 0.01x diamond crystals about 0.5-1.5%

Another diamond feedstock example is provided in the table below.

TABLE 7 EXAMPLE TRIIMODAL DIAMOND FEEDSTOCK MATERIAL AMOUNT Size xdiamond crystals about 80-90% Size 0.1x diamond crystals about 10-20%Size 0.01x diamond crystals about 0-2%

In some embodiments of the invention, the diamond feedstock used will bediamond powder having a greatest dimension of about 100 nanometers orless. In some embodiments of the invention it is preferred to includesome solvent-catalyst metal with the diamond feedstock to aid in thesintering process, although in many applications there will be asignificant solvent-catalyst metal sweep from the substrate duringsintering as well.

d. Solvent Metal Selection

It has already been mentioned that solvent metal will sweep from thesubstrate through the diamond feedstock during sintering in order tosolvate some diamond crystals so that they may later recrystallize andform a diamond-diamond bonded lattice network that characterizespolycrystalline diamond. It is preferred, however, to include somesolvent-catalyst metal in the diamond feedstock only when required tosupplement the sweep of solvent-catalyst metal from the substrate.

Traditionally, cobalt, nickel and iron have been used as solvent metalsfor making polycrystalline diamond. In prosthetic joints, however, thesolvent metal must be biocompatible. The inventors prefer use of asolvent metal such as CoCrMo or CoCrW. Platinum and other materialscould also be used for a binder.

It is important not just to add the solvent metal to diamond feedstock,but also to include solvent metal in an appropriate proportion and tomix it evenly with the feedstock. The inventors prefer the use of about86% diamond feedstock and 15% solvent metal by mass (weight), butanticipate that useful ratios of diamond feedstock to solvent metal willinclude 5:95, 10:90, 20:80, 30:70, 40:60, 50:50, 60:40, 65:35, 75:25,80:20, 90:10, 95:5, 97:3, 98:2, 99:1, 99.5:0.5, 99.7:0.3, 99.8:0.2,99.9:0.1 and others.

In order to mix the diamond feedstock with solvent-catalyst metal, firstthe amounts of feedstock and solvent metal to be mixed may be placedtogether in a mixing bowl, such as a mixing bowl made of the desiredsolvent-catalyst metal. Then the combination of feedstock and solventmetal may be mixed at an appropriate speed (such as 200 rpm) with drymethanol and attritor balls for an appropriate time period, such as 30minutes. The attritor balls, the mixing fixture and the mixing bowl arepreferably made from the solvent-catalyst metal. The methanol may thenbe decanted and the diamond feedstock separated from the attritor balls.The feedstock may then be dried and cleaned by firing in a molecularhydrogen furnace at about 1000 degrees Celsius for about 1 hour. Thefeedstock is then ready for loading and sintering. Alternatively, it maybe stored in conditions which will preserve its cleanliness. Appropriatefurnaces which may be used for firing also include hydrogen plasmafurnaces and vacuum furnaces.

e. Loading Diamond Feedstock

The loading technique for diamond feedstock used is critical to thesuccess of the final product. As mentioned previously, the diamondfeedstock must be loaded to uniform density in order to produce acomponent that lacks unwanted distortion.

Referring to FIG. 7, an apparatus for carrying out a preferred loadingtechnique is depicted. The apparatus includes a spinning rod 701 with alongitudinal axis 702, the spinning rod being capable of spinning aboutits longitudinal axis. The spinning rod 701 has an end 703 matched tothe size and shape of the part to be manufactured. For example, if thepart to be manufactured is a femoral head or an acetabular cup, thespinning rod end 703 should be hemispherical.

A compression ring 704 is provided with a bore 705 through which thespinning rod 701 may project. A die 706 or can is provided with a cavity707 also matched to the size and shape of the part to be made.

In order to load diamond feedstock, the spinning rod is placed into adrill chuck and the spinning rod is aligned with the center point of thedie. The depth to which the spinning rod stops in relation to the cavityof the die is controlled with a set screw and monitored with a dialindicator.

The die is charged with a known amount of diamond feedstock material.The spinning rod is then spun about its longitudinal axis and loweredinto the die cavity to a predetermined depth. The spinning rod contactsand rearranges the diamond feedstock during this operation. Then thespinning of the spinning rod is stopped and the spinning rod is lockedin place.

The compression ring is then lowered around the outside of the spinningrod to a point where the compression ring contacts diamond feedstock inthe cavity of the die. The part of the compression ring that contactsthe diamond is annular. The compression ring is tamped up and down tocompact the diamond. This type of compaction is used to distributediamond material throughout the cavity to the same density and may bedone in stages to prevent bridging. Packing the diamond with thecompaction ring causes the density of the diamond around the equator ofthe sample caused to be very uniform and the same as that of the polarregion in the cavity. In this configuration, the diamond sinters in atruly spherical fashion and the resulting part maintains its sphericityto close tolerances.

Another method which may be employed to maintain a uniform density ofthe feedstock diamond is the use of a binder. A binder is added to thecorrect volume of feedstock diamond, and then the combination is pressedinto a can. Some binders which might be used include polyvinyl butyryl,polymethyl methacrylate, polyvinyl formol, polyvinyl chloride acetate,polyethylene, ethyl cellulose, methylabietate, paraffin wax,polypropylene carbonate and polyethyl methacrylate.

In a preferred embodiment of the invention, the process of bindingdiamond feedstock includes four steps. First, a binder solution isprepared. A binder solution may be prepared by adding about 5 to 25%plasticizer to pellets of poly(propylene carbonate), and dissolving thismixture in solvent such as 2-butanone to make about a 20% solution byweight.

Plasticizers that may be used include nonaqueous binders generally,glycol, dibutyl phthalate, benzyl butyl phthalate, alkyl benzylphthalate, diethylhexyl phthalate, diisoecyl phthalate, diisononylphthalate, dimethyl phthalate, dipropylene glycol dibenzoate, mixedglycols dibenzoate, 2-ethylhexyl diphenyl dibenzoate, mixed glycolsdibenzoate, 2-ethylhexyl diphenyl phosphate, isodecyl diphenylphosphate, isodecyl diphenl phosphate, tricrestyl phosphate, tributoxyethyl phosphate, dihexyl adipate, triisooctyl trimellitate, dioctylphthalate, epoxidized linseed oil, epoxidized soybean oil, acetyltriethyl citrate, propylene carbonate, various phthalate esters, butylstearate, glycerin, polyalkyl glycol derivatives, diethyl oxalate,paraffin wax and triethylene glycol. Other appropriate plasticizers maybe used as well.

Solvents that may be used include 2-butanone, methylene chloride,chloroform, 1,2-dichloroethne, trichlorethylene, methyl acetate, ethylacetate, vinyl acetate, propylene carbonate, n-propyl acetate,acetonitrile, dimethylformamide, propionitrile, n-mehyl-2-pyrrolidene,glacial acetic acid, dimethyl sulfoxide, acetone, methyl ethyl ketone,cyclohexanone, oxysolve 80a, caprotactone, butyrolactone,tetrahydrofuran, 1,4 dioxane, propylene oxide, cellosolve acetate,2-methoxy ethyl ether, benzene, styrene, xylene, ethanol, methanol,toluene, cyclohexane, chlorinated hydrocarbons, esters, ketones, ethers,ethyl benzene and various hydrocarbons. Other appropriate solvents maybe used as well.

Second, diamond is mixed with the binder solution. Diamond may be addedto the binder solution to achieve about a 2-25% binder solution (thepercentage is calculated without regard to the 2-butanone).

Third, the mixture of diamond and binder solution is dried. This may beaccomplished by placing the diamond and binder solution mixture in avacuum oven for about 24 hours at about 50 degrees Celsius in order todrive out all of the solvent 2-butanone. Fourth, the diamond and bindermay be pressed into shape. When the diamond and binder is removed fromthe oven, it will be in a clump that may be broken into pieces which arethen pressed into the desired shape with a compaction press. A pressingspindle of the desired geometry may be contacted with the bound diamondto form it into a desired shape. When the diamond and binder have beenpressed, the spindle is retracted. The preferred final density ofdiamond and binder after pressing is at least about 2.6 grams per cubiccentimeter.

If a volatile binder is used, it should be removed from the shapeddiamond prior to sintering. The shaped diamond is placed into a furnaceand the binding agent is either gasified or pyrolized for a sufficientlength of time such that there is no binder remaining.

Polycrystalline diamond compact quality is reduced by foreigncontamination of the diamond or substrate, and great care must be takento ensure that contaminants and binder are removed during the furnacecycle. Ramp up and the time and temperature combination are critical foreffective pyrolization of the binder. For the binder example givenabove, the debinding process preferably used to remove the binder is asfollows. Reviewing FIG. 7A while reading this description may behelpful.

First, the shaped diamond and binder are heated to from ambienttemperature to about 500 degrees Celsius. The temperature is preferablyincreased by about 2 degrees Celsius per minute until about 500 degreesCelsius is reached. Second, the temperature of the bound and shapeddiamond is maintained at about 500 degrees Celsius for about 2 hours.Third, the temperature of the diamond is increased again. Thetemperature is preferably increased from about 500 degrees Celsius byabout 4 degrees per minute until a temperature of about 950 degreesCelsius is reached. Fourth, the diamond is maintained at about 950degrees Celsius for about 6 hours. Fifth, the diamond is then permittedto return to ambient temperature at a temperature decrease of about 2degrees per minute.

In some embodiments of the invention, it may be desirable to preformbound diamond feedstock by an appropriate process, such as injectionmolding. The diamond feedstock may include diamond crystals of one ormore sizes, solvent-catalyst metal, and other ingredients to controldiamond recrystallization and solvent-catalyst metal distribution.Handling the diamond feedstock is not difficult when the desired finalcurvature of the part is flat, convex dome or conical. However, when thedesired final curvature of the part has complex contours, such asillustrated herein, providing uniform thickness and accuracy of contoursof the polycrystalline diamond compact is more difficult when usingpowder diamond feedstock. In such cases it may be desirable to performthe diamond feedstock before sintering.

If it is desired to perform diamond feedstock prior to loading into acan for sintering, rather than placing powder diamond feedstock into thecan, the steps described herein and variations of them may be followed.First, as already described, a suitable binder is added to the diamondfeedstock. Optionally, powdered solvent-catalyst metal and othercomponents may be added to the feedstock as well. The binder willtypically be a polymer chosen for certain characteristics, such asmelting point, solubility in various solvents, and CTE. One or morepolymers may be included in the binder. The binder may also include anelastomer and/or solvents as desired in order to achieve desiredbinding, fluid flow and injection molding characteristics. The workingvolume of the binder to be added to a feedstock preferably will be equalto or slightly more than the measured volume of empty space in aquantity of lightly compressed powder. Since binders typically consistof materials such as organic polymers with relatively high CTE's, theworking volume should be calculated for the injection moldingtemperatures expected. The binder and feedstock should be mixedthoroughly to assure uniformity of composition. When heated, the binderand feedstock will have sufficient fluid character to flow in highpressure injection molding. The heated feedstock and binder mixture isthen injected under pressure into molds of desired shape. The moldedpart then cools in the mold until set, and the mold can then be openedand the part removed. Depending on the final polycrystalline diamondcompact geometry desired, one or more molded diamond feedstock componentcan be created and placed into a can for polycrystalline diamond compactsintering. Further, use of this method permits diamond feedstock to bemolded into a desired form and then stored for long periods of timeprior to use in the sintering process, thereby simplifying manufacturingand resulting in more efficient production.

As desired, the binder may be removed from the injection molded diamondfeedstock form. A variety of methods are available to achieve this. Forexample, by simple vacuum or hydrogen furnace treatment, the binder maybe removed from the diamond feedstock form. In such a method, the formwould be brought up to a desired temperature in a vacuum or in a verylow pressure hydrogen (reducing) environment. The binder will thenvolatilize with increasing temperature and will be removed from theform. The form may then be removed from the furnace. When hydrogen isused, it helps to maintain extremely clean and chemically activesurfaces on the diamond crystals of the diamond feedstock form.

An alternative method for removing the binder from the form involvesutilizing two or polymer (such as polyethylene) binders with differentmolecular weights. After initial injection molding, the diamondfeedstock form is placed in a solvent bath which removes the lowermolecular weight polymer, leaving the higher molecular weight polymer tomaintain the shape of the diamond feedstock form. Then the diamondfeedstock form is placed in a furnace for vacuum or very low pressurehydrogen treatment for removal of the higher molecular weight polymer.

Partial or complete binder removal from the diamond feedstock form maybe performed prior to assembly of the form in a pressure assembly forpolycrystalline diamond compact sintering. Alternatively, the pressureassembly including the diamond feedstock form may be placed into afurnace for vacuum or very low pressure hydrogen furnace treatment andbinder removal.

Diamond feedstock may be selected and loaded in order to createdifferent types of gradients in the diamond table. These include aninterface gradient diamond table, an incremental gradient diamond table,and a continuous gradient diamond table.

If a single type or mix of diamond feedstock is loaded adjacent asubstrate, as discussed elsewhere herein, sweep of solvent-catalystmetal through the diamond will create an interface gradient in thegradient transition zone of the diamond table.

An incremental gradient diamond table may be created by loading diamondfeedstocks of differing characteristics (diamond particle size, diamondparticle distribution, metal content, etc.) in different strata orlayers before sintering.. For example, a substrate is selected, and afirst diamond feedstock containing 60% solvent-catalyst metal by weightis loaded in a first strata adjacent the substrate. Then a seconddiamond feedstock containing 40% solvent-catalyst metal by weight isloaded in a second strata adjacent the first strata. Optionally,additional strata of diamond feedstock may be used. For example, a thirdstrata of diamond feedstock containing 20% solvent-catalyst metal byweight may be loaded adjacent the second strata.

A continuous gradient diamond table may be created by loading diamondfeedstock in a manner that one or more of its characteristicscontinuously vary from one depth in the diamond table to another. Forexample, diamond particle size may vary from large near a substrate (inorder to create large interstitial spaces in the diamond forsolvent-catalyst metal to sweep into) to small near the diamond bearingsurface in order to create a part that is strongly bonded to thesubstrate but that has a very low friction bearing surface.

The diamond feedstocks of the different strata may be of the same ordifferent diamond particle size and distribution. Solvent-catalyst metalmay be included in the diamond feedstock of the different strata inweight percentages of from about 0% to more than about 80%. In someembodiments, diamond feedstock will be loaded with no solvent-catalystmetal in it, relying on sweep of solvent-catalyst metal from thesubstrate to achieve sintering. Use of a plurality of diamond feedstockstrata, the strata having different diamond particle size anddistribution, different solvent-catalyst metal by weight, or both,allows a diamond table to be made that has different physicalcharacteristics at the interface with the substrate than at the loadbearing and articulation surface. This allows a polycrystalline diamondcompact to be manufactured which has a diamond table very firmly bondedto its substrate, and which has very favorable characteristics at theload bearing and articulation surface in order to achieve low frictionarticulation, impact resistance, and durability.

f. Reduction of Free Volume in Diamond Feedstock

As mentioned earlier, it may be desirable to remove free volume in thediamond feedstock before sintering is attempted. The inventors havefound this is a useful procedure when producing spherical concave andconvex parts. If a press with sufficient anvil travel is used for highpressure and high temperature sintering, however, this step may not benecessary. Preferably free volume in the diamond feedstock will bereduced so that the resulting diamond feedstock is at least about 95%theoretical density and preferably closer to about 97% of theoreticaldensity.

Referring to FIGS. 8 and 8A, an assembly used for precompressing diamondto eliminate free volume is depicted. In the drawing, the diamondfeedstock is intended to be used to make a convex sphericalpolycrystalline diamond part. The assembly may be adapted forprecompressing diamond feedstock for making polycyrstalline diamondcompacts of other complex shapes.

The assembly depicted includes a cube 801 of a pressure transfer medium.A cube is made from pyrophillite or other appropriate pressure transfermaterial such as a synthetic pressure medium and is intended to undergopressure from a cubic press with anvils simultaneously pressing the sixfaces of the cube. A cylindrical cell rather than a cube would be usedif a belt press were utilized for this step.

The cube 801 has a cylindrical cavity 802 or passage through it. Thecenter of the cavity 802 will receive a spherical refractory metal can810 loaded with diamond feedstock 806 that is to be precompressed. Thediamond feedstock 806 may have a substrate with it.

The can 810 consists of two hemispherical can halves 810 a and 810 b,one of which overlaps the other to form a slight lip 812. The can ispreferably an appropriate refractory metal such as niobium, tantalum,molybdenum, etc. The can is typically two hemispheres, one which isslightly larger to accept the other being slid inside of it to fullyenclosed the diamond feedstock. A rebated area or lip is provided in thelarger can so that the smaller can will satisfactorily fit therein. Theseam of the can is sealed with an appropriate sealant such as dryhexagonal boronitride or a synthetic compression medium. The sealantforms a barrier that prevents the salt pressure medium from penetratingthe can. The can seam may also be welded by plasma, laser, or electronbeam processes.

An appropriately shaped pair of salt domes 804 and 807 surround the can810 containing the diamond feedstock 806. In the example shown, the saltdomes each have a hemispherical cavity 805 and 808 for receiving the can810 containing the spherical diamond feedstock 806. The salt domes andthe can and diamond feedstock are assembled together so that the saltdomes encase the diamond feedstock. A pair of cylindrical salt disks 803and 809 are assembled on the exterior of the salt domes 804 and 807. Allof the aforementioned components fit within the bore 802 of the pressuremedium cube 801.

The entire pyrocube assembly is placed into a press and pressurizedunder appropriate pressure (such as about 40-68 Kbar) and for anappropriate although brief duration to precompress the diamond andprepare it for sintering. No heat is necessary for this step.

g. Prepare Heater Assembly

In order to sinter the assembled and loaded diamond feedstock describedabove into polycrystalline diamond, both heat and pressure are required.Heat is provided electrically as the part undergoes pressure in a press.A prior art heater assembly is used to provide the required heat.

A refractory metal can containing loaded and precompressed diamondfeedstock is placed into a heater assembly. Salt domes are used toencase the can. The salt domes used are preferably white salt (NaCl)that is precompressed to at least about 90-95% of theoretical density.This density of the salt is desired to preserve high pressures of thesintering system and to maintain geometrical stability of themanufactured part. The salt domes and can are placed into a graphiteheater tube assembly. The salt and graphite components of the heaterassembly are preferably baked in a vacuum oven at greater than 100degrees Celsius and at a vacuum of at least 23 torr for about 1 hour inorder to eliminate adsorped water prior to loading in the heaterassembly . Other materials which may be used in construction of a heaterassembly include solid or foil graphite, amorphous carbon, pyroliticcarbon, refractory metals and high electrical resistant metals.

Once electrical power is supplied to the heater tube, it will generateheat required for polycrystalline diamond formation in the highpressure/high temperature pressing operation.

h. Preparation of Pressure Assembly for Sintering

Once a heater assembly has been prepared, it is placed into a pressureassembly for sintering in a press under high pressure and hightemperature. A cubic press or a belt press may be used for this purpose,with the pressure assembly differing somewhat depending on the type ofpress used. The pressure assembly is intended to receive pressure from apress and transfer it to the diamond feedstock so that sintering of thediamond may occur under isostatic conditions.

If a cubic press is used, then a cube of suitable pressure transfermedia such as pyrophillite will contain the heater assembly. Cellpressure medium would be used if sintering were to take place in a beltpress. Salt may be used as a pressure transfer media between the cubeand the heater assembly. Thermocouples may be used on the cube tomonitor temperature during sintering. The cube with the heater assemblyinside of it is considered a pressure assembly, and is place into apress a press for sintering.

i. Sintering of Feedstock into Polycrystalline Diamond

The pressure assembly described above containing a refractory metal canthat has diamond feedstock loaded and precompressed within is placedinto an appropriate press. The type of press preferably used at the timeof the invention is a cubic press (i.e., the press has six anvil faces)for transmitting high pressure to the assembly along 3 axes from sixdifferent directions. Alternatively, a belt press and a cylindrical cellcan be used to obtain similar results. Referring to FIG. 8B, arepresentation of the 6 anvils of a cubic press 820 is provided. Theanvils 821, 822, 823, 824, 825 and 826 are situated around a pressureassembly 830.

To prepare for sintering, the entire pressure assembly is loaded into acubic press and initially pressurized to about 40-68 Kbars. The pressureto be used depends on the product to be manufactured and must bedetermined empirically. Then electrical power is added to the pressureassembly in order to reach a temperature preferably in the range of lessthan about 1145 or 1200 to more than about 1500 degrees Celsius.Preferably about 5800 watts of electrical power is available at twoopposing anvil faces, creating the current flow required for the heaterassembly to generate the desired level of heat. Once the desiredtemperature is reached, the pressure assembly is subjected to pressureof about 1 million pounds per square inch at the anvil face. Thecomponents of the pressure assembly transmit pressure to the diamondfeedstock. These conditions are maintained for preferably about 3-12minutes, but could be from less than 1 minute to more than 30 minutes.The sintering of polycrystalline diamond compacts takes place in anisostatic environment where the pressure transfer components arepermitted only to change in volume but are not permitted to otherwisedeform. Once the sintering cycle is complete, about a 90 second cooldown period is allowed, and then pressure is removed. Thepolycrystalline diamond compact is then removed for finishing.

Removal of a sintered polycrystalline diamond compact having a curved,compound or complex shape from a pressure assembly is simple due to thedifferences in material properties between diamond and the surroundingmetals in preferred embodiments of the invention. This is generallyreferred to as the mold release system of the invention.

One or more of the following component processes is incorporated intothe mold release system:

1) An intermediate layer of material between the polycrystalline diamondcompact part and the mould that prevents bonding of the polycrystallinediamond compact to the mould surface.

2) A mold material that does not bond to the polycrystalline diamondcompact under the conditions of synthesis.

3) A mold material that, in the final stages of, or at the conclusionof, the polycrystalline diamond compact synthesis cycle either contractsaway from the polycrystalline diamond compact in the case of a netconcave polycrystalline diamond compact geometry, or expands away fromthe polycrystalline diamond compact in the case of a net convexpolycrystalline diamond compact geometry.

4) The mold shape can also act, simultaneously as a source of sweepmetal useful in the polycrystalline diamond compact synthesis process.

As an example, below is a discussion of use of a mold release system inmanufacturing a polycrystalline diamond compact by employing a negativeshape of the desired geometry to produce hemispherical cups. The moldsurface contracts away from the final net concave geometry, the moldsurface acts as a source of solvent-catalyst metal for thepolycrystalline diamond compact synthesis process, and the mold surfacehas poor bonding properties to polycrystalline diamond compacts.

In the case of forming concave hemispherical cups such as are used forarticulating surfaces in ball and socket joints, two different methodshave been employed. In the first method, one, a mold consisting of acobalt chrome (ASTM F-799) ball is used as a substrate around which alayer of polycrystalline diamond compact feedstock material is placed,contained by an outer can. A separator ring composed of a material suchas mica or compressed hexagonal boron nitride (HBN) is positioned at thehemisphere of the mold ball to allow separation of the two concavehemispherical polycrystalline diamond compact parts at the conclusion ofthe synthesis process. During the polycrystalline diamond compactsynthesis process, the cobalt-chrome ball expands in size due to theincrease in temperature intrinsic to the process. It also can supplysolvent-catalyst sweep metal to the polycrystalline diamond compactsynthesis process.

After the polycrystalline diamond compact shell has formed around themold ball, the ball separates from the two hemispherical polycrystallinediamond compact cups as it contracts on cooling and pressure reduction.The forces of the shrinking CoCr ball will exceed the bond strength ofdiamond to the CoCr, providing a fairly clean separation and a smoothpolycrystalline diamond cup adjacent a detached spherical CoCr ball.

As an alternative, it is possible to use an intermediate layer ofmaterial between the polycrystalline diamond compact part and the moldsurface. The intermediate material should be a material which contractsaway from the final net concave polycrystalline diamond compact geometryto achieve mold separation with the polycrystalline diamond compact.

The second mold release method for use in forming a hemispherical cup issimilar to the first method. However, in the second method, the mold isa cobalt-cemented tungsten carbide ball or sphere that has been coatedwith a thin layer of hexagonal boron nitride. During the polycrystallinediamond compact synthesis process, the tungsten carbide ball expands insize due to the increase in temperature intrinsic to the process. Afterthe polycrystalline diamond compact shell has formed around the moldball, the mold ball separates from the two hemispherical polycrystallinediamond compact cups as it contracts on cooling. The hexagonal boronnitride prevents bonding between the polycrystalline diamond compactlayer and the tungsten carbide ball and a clean separation is achieved.

Removal of Solvent-Catalyst Metal from PCD

If desired, the solvent-catalyst metal remaining in interstitial spacesof the sintered polycrystalline diamond may be removed. Such removal isaccomplished by chemical leaching as is known in the art. Aftersolvent-catalyst metal has been removed from the interstitial spaces inthe diamond table, the diamond table will have greater stability at hightemperatures. This is because there is no catalyst for the diamond toreact with and break down. Removal of solvent-catalyst metal frominterstitial spaces in the diamond may also be desirable if thesolvent-catalyst material is not biocompatible.

After leaching solvent-catalyst metal from the diamond table, it may bereplaced by another metal, metal or metal compound in order to formthermally stable diamond that is stronger than leached polycrystallinediamond. If it is intended to weld synthetic diamond or apolycrystalline diamond compact to a substrate or to another surfacesuch as by inertia welding, it may be desirable to use thermally stablediamond due to its resistance to heat generated by the welding process.

3. Finishing Methods and Apparatuses

Once a polycrystalline diamond compact has been sintered, a mechanicalfinishing process is preferably employed to prepare the final product.The preferred finishing steps explained below are described with respectto finishing a polycrystalline diamond compact, but they could be usedto finish any other bearing surface or any other type of component.

Prior to the invention herein, the synthetic diamond industry was facedwith the problem of finishing flat surfaces and thin edges of diamondcompacts. Methods for removal of large amounts of diamond from sphericalsurfaces or finishing those surfaces to high degrees of accuracy forsphericity, size and surface finish had not been developed in the priorart.

a. Finishing of Superhard Cylindrical and Flat Forms.

In order to provide a greater perspective on the most preferredfinishing techniques for curved and spherical superhard surfaces, adescription of other finishing techniques is provided.

1.) Lapping.

A wet slurry of diamond grit on cast iron or copper rotating plates areused to remove material on larger flat surfaces (e.g., up to about 70mm. in diameter). End coated cylinders of size ranging from about 3 mmto about 70 mm may also be lapped to create flat surfaces. Lapping isgenerally slow and not dimensionally controllable for depth and layerthickness, although flatness and surface finishes can be held to veryclose tolerances.

2.) Grinding.

Diamond impregnated grinding wheels are used to shape cylindrical andflat surfaces. Grinding wheels are usually resin bonded in a variety ofdifferent shapes depending on the type of material removal required(i.e., cylindrical centerless grinding or edge grinding).Polycrystalline diamond compacts are difficult to grind, and largepolycrystalline diamond compact surfaces are nearly impossible to grind.Consequently, it is desirable to keep grinding to a minimum, andgrinding is usually confined to a narrow edge or perimeter or to thesharpening of a sized PDC end-coated cylinder or machine tool insert.

3.) Electro Spark Discharge Grinding (EDG).

Rough machining of polycrystalline diamond compact may be accomplishedwith electro spark discharge grinding (“EDG”) on large diameter (e.g.,up to about 70 mm.) flat surfaces. This technology typically involvesthe use of a rotating carbon wheel with a positive electrical currentrunning against a polycrystalline diamond compact flat surface with anegative electrical potential. The automatic controls of the EDG machinemaintain proper electrical erosion of the polycrystalline diamondcompact material by controlling variables such as spark frequency,voltage and others. EDG is typically a more efficient method forremoving larger volumes of diamond than lapping or grinding. After EDG,the surface must be finish lapped or ground to remove what is referredto as the heat affected area or re-cast layer left by EDG.

4.) Wire Electrical Discharge Machining (WEDM).

WEDM is used to cut superhard parts of various shapes and sizes fromlarger cylinders or flat pieces. Typically, cutting tips and inserts formachine tools and reshaping cutters for oil well drilling bits representthe greatest use for WEDM in PDC finishing.

5.) Polishing.

Polishing superhard surfaces to very high tolerances may be accomplishedby diamond impregnated high speed polishing machines. The combination ofhigh speed and high friction temperatures tends to burnish a PDC surfacefinished by this method, while maintaining high degrees of flatness,thereby producing a mirror-like appearance with precise dimensionalaccuracy.

b. Finishing A Spherical Geometry.

Finishing a spherical surface (concave spherical or convex spherical)presents a greater problem than finishing a flat surface or the roundededge of a cylinder. The total surface area of a sphere to be finishedcompared to the total surface area of a round end of a cylinder of likeradius is four (4) times greater, resulting in the need to remove four(4) times the amount of polycrystalline diamond compact material. Thenature of a spherical surface makes traditional processing techniquessuch as lapping, grinding and others unusable because they are adaptedto flat and cylindrical surfaces. The contact point on a sphere shouldbe point contact that is tangential to the edge of the sphere, resultingin a smaller amount of material removed per unit of time, and aproportional increase in finishing time required. Also, the design andtypes of processing equipment and tooling required for finishingspherical objects must be more accurate and must function to closertolerances than those for other shapes. Spherical finishing equipmentalso requires greater degrees of adjustment for positioning theworkpiece and tool ingress and egress.

The following are steps that may be performed in order to finish aspherical, rounded or arcuate surface.

1.) Rough Machining.

It is preferred to initially rough out the dimensions of the surfaceusing a specialized electrical discharge machining apparatus. Referringto FIG. 9, roughing a polycrystalline diamond compact sphere 903 isdepicted. A rotator 902 is provided that is continuously rotatable aboutits longitudinal axis (the z axis depicted). The sphere 903 to beroughed is attached to a spindle of the rotator 902. An electrode 901 isprovided with a contact end 901A that is shaped to accommodate the partto be roughed. In this case the contact end 901 A has a partiallyspherical shape. The electrode 901 is rotated continuously about itslongitudinal axis (the y axis depicted). Angular orientation of thelongitudinal axis y of the electrode 901 with respect to thelongitudinal axis z of the rotator 902 at a desired angle β is adjustedto cause the electrode 901 to remove material from the entire sphericalsurface of the ball 903 as desired.

Thus, the electrode 901 and the sphere 903 are rotating about differentaxes. Adjustment of the axes can be used to achieve near perfectspherical movement of the part to be roughed. Consequently, a nearlyperfect spherical part results from this process. This method producespolycrystalline diamond compact spherical surfaces with a high degree ofsphericity and cut to very close tolerances. By controlling the amountof current introduced to the erosion process, the depth and amount ofthe heat affected zone can be minimized. In the case of apolycrystalline diamond compact, the heat affected zone can be kept toabout 3 to 5 microns in depth and is easily removed by grinding andpolishing with diamond impregnated grinding and polishing wheels.

Referring to FIG. 10, roughing a convex spherical polycrystallinediamond compact 1003 such as an acetablular cup is depicted. A rotator1002 is provided that is continuously rotatable about its longitudinalaxis (the z axis depicted). The part 1003 to be roughed is attached to aspindle of the rotator 1002. An electrode 1000 is provided with acontact end 1001 A that is shaped to accommodate the part to be roughed.The electrode 1001 is continuously rotatable about its longitudinal axis(the y axis depicted). Angular orientation of the longitudinal axis y ofthe electrode 1001 with respect to the longitudinal axis z of therotator 1002 at a desired angle βis adjusted to cause the electrode 1001to remove material from the entire spherical surface of the cup 1003 asdesired.

In some embodiments of the invention, multiple electro discharge machineelectrodes will be used in succession in order to machine a part. Abattery of electro discharge machines may be employed to carry this outin assembly line fashion.

2) Finish Grinding and Polishing.

Once the spherical surface (whether concave or convex) has been roughmachined as described above or by other methods, finish grinding andpolishing of a part can take place. Grinding is intended to remove theheat affected zone in the polycrystalline diamond compact material leftbehind by electrodes. Use of the same rotational geometry as depicted inFIGS. 9 and 10 allows sphericity of the part to be maintained whileimproving its surface finish characteristics.

Referring to FIG. 11, it can be seen that a rotator 1101 holds a part tobe finished 1103, in this case a convex sphere, by use of a spindle. Therotator 110 1 is rotated continuously about its longitudinal axis (the zaxis). A grinding or polishing wheel 1102 is provided is rotatedcontinuously about its longitudinal axis (the x axis). The moving part1103 is contacted with the moving grinding or polishing wheel 1102. Theangular orientation β of the rotator 1101 with respect to the grindingor polishing wheel 1102 may be adjusted and oscillated to effectgrinding or polishing of the part (ball or socket) across its entiresurface and to maintain sphericity.

Referring to FIG. 12, it can be seen that a rotator 1201 holds a part tobe finished 1203, in this case a convex spherical cup, by use of aspindle. The rotator 1201 is rotated continuously about its longitudinalaxis (the z axis). A grinding or polishing wheel 1202 is provided thatis continuously rotatable about its longitudinal axis (the x axis). Themoving part 1203 is contacted with the moving grinding or polishingwheel 1202. The angular orientation B of the rotator 1201 with respectto the grinding or polishing wheel 1202 may be adjusted and oscillatedif required to effect grinding or polishing of the part across thespherical portion of it surface.

In the preferred embodiment of the invention, grinding utilizes a gritsize ranging from 100 to 150 according to standard ANSI B74.16-1971 andpolishing utilizes a grit size ranging from 240 to 1500, although gritsize may be selected according to the user's preference. Wheel speed forgrinding should be adjusted by the user to achieve a favorable materialremoval rate, depending on grit size and the material being ground. Asmall amount of experimentation can be used to determine appropriatewheel speed for grinding.

As desired in the invention, a diamond abrasive hollow grill may be usedfor polishing diamond or superhard bearing surfaces. A diamond abrasivehollow grill includes a hollow tube with a diamond matrix of metal,ceramic and resin (polymer) is found.

If a diamond surface is being polished, then the wheel speed forpolishing preferably will be adjusted to cause a temperature increase orheat buildup on the diamond surface. This heat buildup will causeburnishing of the diamond crystals to create a very smooth andmirror-like low friction surface. Actual material removal duringpolishing of diamond is not as important as removal sub-micron sizedasperities in the surface by a high temperature burnishing action ofdiamond particles rubbing against each other. A surface speed of 6000feet per minute minimum is generally required together with a highdegree of pressure to carry out burnishing. Surface speeds of 4000 to10,000 feet per minute are believed to be the most desirable range.Depending on pressure applied to the diamond being polished, polishingmay be carried out at from about 500 linear feet per minute and 20,000linear feet per minute.

Pressure must be applied to the workpiece in order to raise thetemperature of the part being polished and thus to achieve the mostdesired mirror-like polish, but temperature should not be increased tothe point that it causes complete degradation of the resin bond thatholds the diamond polishing wheel matrix together, or resin will bedeposited on the diamond. Excessive heat will also unnecessarily degradethe surface of the diamond.

Maintaining a constant flow of coolant (such as water) across thediamond surface being polished, maintaining an appropriate wheel speedsuch as 6000 linear feet per minute, applying sufficient pressureagainst the diamond to cause heat buildup but not so much as to degradethe wheel or damage the diamond, and timing the polishing appropriatelyare all important and must all be determined and adjusted according tothe particular equipment being used and the particular part beingpolished. Generally the surface temperature of the diamond beingpolished should not be permitted to rise above 800 degrees Celsius orexcessive degradation of the diamond will occur. Desirable surfacefinishing of the diamond, called burnishing, generally occurs between650 and 750 degrees Celsius.

During polishing it is important to achieve a surface finish that hasthe lowest possible coefficient of friction, thereby providing a lowfriction and long-lasting articulation surface. Preferably, once adiamond or other superhard surface is formed in a prosthetic joint, thesurface is then polished to an Ra value of 0.3 to 0.005 microns.Acceptable polishing will include an Ra value in the range of 0.5 to0.005 microns or less. The parts of the joint may be polishedindividually before assembly or as a unit after assembly. Other methodsof polishing polycrystalline diamond compacts and other superhardmaterials could be adapted to work with the articulation surfaces of theinvented joints, with the objective being to achieve a smooth surface,preferably with an Ra value of 0.01-0.005 microns.

In order to select two matching prosthetic joint halves for shipment andimplantation in a patient, it is preferred that precise measurement ofthe opposing bearing surfaces be taken at 98.6 degrees Fahrenheit(normal body temperature) in order to match joint halves withappropriate dimensions.

Structures manufactured according to the principles of the invention setforth above will provide strong and durable low friction bearingsurfaces for a variety of uses including prosthetic joints.

While the present invention has been described and illustrated inconjunction with a number of specific embodiments, those skilled in theart will appreciate that variations and modifications may be madewithout departing from the principles of the invention as illustratedherein and as claimed. The present invention may be embodied in otherspecific forms without departing from its spirit or essentialcharacteristics. The described embodiments are to be considered in allrespects as only illustrative, and not restrictive. The scope of theinvention is, therefore, indicated by the appended claims, rather thanby the foregoing description. All changes that come within the meaningand range of equivalency of the claims are to be embraced within theirscope.

We claim:
 1. A prosthetic joint comprising: a first joint member, afirst joint member bone fixation portion, said first joint member bonefixation portion being adapted to be securable to a bone, a first jointmember load bearing and articulation portion, a first joint memberpolycrystalline diamond compact, said first joint member polycrystallinediamond compact serving to form at least a portion of said first jointmember load bearing and articulation portion, a first joint memberpolycrystalline diamond compact substrate, said substrate being locatedon said first joint member polycrystalline diamond compact, a firstjoint member polycrystalline diamond compact diamond table sintered tosaid first joint member polycrystalline diamond compact substrate,solvent-catalyst metal located in said first joint memberpolycrystalline diamond compact, a first joint member gradienttransition zone between said first joint member polycrystalline diamondcompact substrate and said first joint member polycrystalline diamondcompact diamond table, said first joint member gradient transition zonehaving a substrate side and a diamond table side, said first jointmember gradient transition zone having both solvent-catalyst metal anddiamond therein, and said first joint member gradient transition zoneexhibiting a transition of ratios of percentage content ofsolvent-catalyst metal to diamond from one side of said gradienttransition zone to another side such that at a first point in said firstjoint member gradient transition zone near said substrate side, theratio of percentage content of solvent-catalyst metal to diamond isgreater than it is at a second point in said first joint member gradienttransition zone closer to said diamond side than said first point,chemical bonds between said first joint member polycrystalline diamondcompact diamond table and said first joint member polycrystallinediamond compact substrate which tend to secure said diamond table tosaid substrate, a mechanical grip between said first joint memberpolycrystalline diamond compact diamond table and said first jointmember polycrystalline diamond compact substrate which tends to securesaid diamond table to said substrate, a first joint member load bearingand articulation surface, said first joint member load bearing andarticulation surface including sintered polycrystalline diamond of saidfirst joint member polycrystalline diamond compact, said sinteredpolycrystalline diamond providing a smooth and low-friction first jointmember load bearing and articulation surface, a second joint member, asecond joint member bone fixation portion, said second joint member bonefixation portion being adapted to be securable to a bone, a second jointmember load bearing and articulation portion, and a second joint memberload bearing and articulation surface, said second joint member loadbearing and articulation surface being shaped to contact said firstjoint member load bearing and articulation surface and to permitarticulation therewith.
 2. A joint as recited in claim 1 furthercomprising topographical features on at least one of said substrates,said topographical features serving to enhance said mechanical gripbetween the substrate and its corresponding diamond table.
 3. A joint asrecited in claim 1 wherein at least one of said first and said secondjoint member load bearing and articulation surfaces has a convex shapeand wherein at least one of said first and said second joint member loadbearing and articulation surfaces has a concave shape.
 4. A joint asrecited in claim 1 wherein at least one of said first and said secondjoint member load bearing and articulation surface has an arcuate shape.5. A joint as recited in claim 1 wherein at least one of said first andsaid second joint member load bearing and articulation surface has ahemispherical shape.
 6. A joint as recited in claim 1 further comprisingan interface present between said substrate and said diamond table.
 7. Ajoint as recited in claim 1 further comprising solvent-catalyst metalpresent in said substrate.
 8. A joint as recited in claim 7 wherein saidsolvent-catalyst metal present in said substrate is the samesolvent-catalyst metal present in said diamond table.
 9. A joint asrecited in claim 1 further comprising interstitial spaces in saiddiamond table.
 10. A joint as recited in claim 1 further comprisingsolvent-catalyst metal located in said diamond table.
 11. A joint asrecited in claim 1 further comprising a residual stress field in saidpolycrystalline diamond compact, said residual stress field tending toenhance strength of said polycrystalline diamond compact.
 12. A joint asrecited in claim 1 wherein diamond in said polycrystalline diamondcompact has a coefficient of thermal expansion CTE_(Cd), and wherein itscorresponding substrate has a coefficient of thermal expansionCTE_(sub), and wherein CTE_(Cd) is not equal to CTE_(sub).
 13. A jointas recited in claim 1 wherein in said polycrystalline diamond compact,the diamond has a modulus M_(Cd), and the substrate has a modulusM_(sub), and wherein M_(Cd) is not equal to M_(sub).
 14. A joint asrecited in claim 1 further comprising a crystalline diamond structure insaid diamond table.
 15. A joint as recited in claim 1 wherein at leastone of said load bearing and articulation surfaces has an Ra value ofbetween about 0.5 to about 0.005 microns.
 16. A joint as recited inclaim 1 wherein of said polycrystalline diamond load bearing andarticulation surface is burnished.
 17. A joint as recited in claim 1wherein at least one of said first and said second joint member bonefixation portions is shaped to be press fit into a receptacle formed ina bone.
 18. A joint as recited in claim 1 wherein at least one of saidfirst and said second joint member bone fixation portions includes abone mating surface on at least a portion of its exterior.
 19. A jointas recited in claim 1 wherein at least one of said first and said secondjoint member bone fixation portions includes a bone mating surface on atleast a portion of its exterior, said bone mating surface including astructure selected from the group consisting of metal mesh, porousmetal, porous diamond, metal sintered beads, and plasma spray metal. 20.A joint as recited in claim 1 wherein at least one of said first andsaid second joint member bone fixation portions includes a bone matingsurface on at least a portion of its exterior that permitsosseointegration.
 21. A joint as recited in claim 1 wherein at least oneof said first and said second joint member bone fixation portionsincludes a bone mating surface on at least a portion of its exteriorthat includes a surface coating which encourages bone growth againstsaid coating.
 22. A joint as recited in claim 21 wherein said coatingincludes hydroxyl apatite.
 23. A joint as recited in claim 1 wherein atleast one of said first and said second joint member bone fixationportions is shaped to permit bone fixation to be accomplished by use ofat least one mechanical fastener.
 24. A joint as recited in claim 1wherein said substrate includes CoCr and wherein CoCr is asolvent-catalyst metal in the formation of said diamond.
 25. A joint asrecited in claim 1 wherein said acetabular cup substrate includes ametal alloy with at least one joint of said metal alloy being selectedfrom the group consisting of titanium, aluminum, vanadium, molybdenum,hafnium, nitinol, cobalt, chrome, molybdenum, tungsten, cementedtungsten carbide, cemented chrome carbide, fused silicon carbide,nickel, tantalum, and stainless steel.
 26. A joint as recited in claim 1wherein said substrate includes a plurality of substrate layers.
 27. Ajoint as recited in claim 1 wherein said substrate includes at least twodistinct substrate layers of different metals.
 28. A joint as recited inclaim 1 wherein said diamond table includes diamond crystals of at leasttwo different dimensions.
 29. A joint as recited in claim 1 furthercomprising a counter bearing material located on said second jointmember load bearing and articulation surface, said counter bearingmaterial having characteristics that permit articulation ofpolycrystalline diamond against it.
 30. A joint as recited in claim 29wherein said counter bearing material includes a material selected fromthe group consisting monocrystal diamond, natural diamond,polycrystalline diamond, CVD diamond, PVD diamond, cubic boron nitride,wurzitic boron nitride, ceramic, cobalt-chrome alloy, titanium alloy,nickel, vanadium, tantalum, hafnium, molybdenum, cemented tungstencarbide, niobium, zirconia ceramic, alumina ceramic, polymers, UHMWPE,PEEK, cross-linked polymers and sapphire.
 31. A prosthetic jointcomprising: a first joint member, a first joint member bone fixationportion, said first joint member bone fixation portion being adapted tobe securable to a bone, a first joint member load bearing andarticulation portion, a first joint member load bearing and articulationsurface, located on said first joint member load bearing andarticulation portion, a second joint member, a second joint member bonefixation portion, said second joint member bone fixation portion beingshaped to be securable to a bone, a second joint member load bearing andarticulation portion, a second joint member load bearing andarticulation surface located on said second joint member load bearingand articulation portion, a volume of superhard material located on saidfirst joint member load bearing and articulation portion, said volume ofsuperhard material forming at least a portion of said first joint memberload bearing and articulation surface, and an articulation surfaceformed by at least a portion of said volume of superhard material, saidarticulation surface being formed to permit low-friction articulation ofsaid second joint member load bearing and articulation surfacethereagainst; wherein said volume of superhard material comprisespolycrystalline diamond and wherein said first joint member load bearingand articulation member comprises a substrate to which at least aportion of said polycrystalline diamond is sintered; wherein saidsuperhard material includes a gradient transition zone betweenpolycrystalline diamond and said substrate; wherein said gradienttransition zone has both solvent-catalyst metal and diamond presenttherein; wherein said gradient transition zone exhibits a gradient ofratios of solvent-catalyst metal to diamond at various points in saidgradient transition zone between said substrate and said load bearingand articulation surface; wherein chemical bonds between saidpolycrystalline diamond and said substrate are found in said gradienttransition zone.
 32. A joint as recited in claim 31 further comprising amechanical grip between said polycrystalline diamond and said substrate.33. A joint as recited in claim 32 wherein further comprisingtopographical features on said substrate, said topographical featuresserving to enhance said mechanical grip between said substrate and saidpolycrystalline diamond.
 34. A joint as recited in claim 31 wherein saidpolycrystalline diamond and said substrate comprise a polycrystallinediamond compact, and further comprising a residual stress field in saidpolycrystalline diamond compact, said residual stress field tending toenhance strength of said polycrystalline diamond compact.
 35. A joint asrecited in claim 31 wherein said polycrystalline diamond has acoefficient of thermal expansion CTE_(Cd), and said substrate has acoefficient of thermal expansion CTE_(sub), and wherein CTE_(Cd) is notequal to CTE_(sub).
 36. A joint as recited in claim 31 wherein in saidpolycrystalline diamond has a modulus M_(Cd) and said substrate has amodulus M_(sub), and wherein M_(Cd) is not equal to M_(sub).
 37. A jointas recited in claim 31 wherein at least one of said load bearing andarticulation surfaces has an Ra value of between about 0.5 to about0.005 microns.
 38. A joint as recited in claim 37 wherein at least aportion of said polycrystalline diamond is burnished.
 39. A joint asrecited in claim 31 wherein said diamond table includes diamond crystalsof at least two different dimensions.
 40. A joint as recited in claim 31further comprising a counter bearing material located on said secondjoint member load bearing and articulation surface, said counter bearingmaterial having characteristics that permit articulation of saidsuperhard material thereagainst.
 41. A joint as recited in claim 31wherein said superhard material is selected from the group consisting ofmonocrystal diamond, natural diamond, polycrystalline diamond, CVDdiamond, PVD diamond, cubic boron nitride, wurzitic boron nitride,ceramic, cobalt-chrome alloy, titanium alloy, nickel, vanadium,tantalum, hafnium, molybdenum, cemented tungsten carbide, niobium,zirconia ceramic, alumina ceramic, polymers, UHMWPE, PEEK, cross-linkedpolymers and sapphire.
 42. A prosthetic joint comprising: a substratethat includes a solvent-catalyst metal, a diamond layer sintered to saidsubstrate, a zone between said substrate and said diamond layer that hasa composition gradient of decreasing solvent-catalyst metal contentacross said zone, chemical bonds in said zone, said chemical bondsincluding diamond-to-diamond bonds in said diamond table,diamond-to-metal bonds in said gradient transition zone, andmetal-to-metal bonds in said solvent-catalyst metal, a mechanical gripbetween said diamond layer and said substrate which tends to secure saiddiamond layer to said substrate, interstitial spaces in said diamondlayer, solvent-catalyst metal present in said interstitial spaces, and anon-planar load bearing and articulation surface formed by said diamondlayer.
 43. A joint as recited in claim 42 wherein sintered diamond insaid diamond layer has a coefficient of thermal expansion CTE_(Cd), andwherein said substrate has a coefficient of thermal expansion CTE_(sub),and wherein CTE_(Cd) is not equal to CTE_(sub).
 44. A joint as recitedin claim 42 wherein said sintered diamond in said diamond layer has amodulus M_(Cd), and wherein said substrate has a modulus M_(sub), andwherein M_(Cd) is not equal to M_(sub).
 45. A joint as recited in claim42 further comprising a residual stress field that tends to enhance thestrength of attachment of said diamond layer to said substrate.
 46. Ajoint as recited in claim 42 further comprising substrate surfacetopographical features on said substrate.
 47. A joint as recited inclaim 42 wherein said substrate includes a metal alloy with at least onejoint of said metal alloy being selected from the group consisting oftitanium, aluminum, vanadium, molybdenum, hafnium, nitinol, cobalt,chrome, molybdenum, tungsten, cemented tungsten carbide, cemented chromecarbide, fused silicon carbide, nickel, tantalum, and stainless steel.48. A joint as recited in claim 42 wherein diamond layer comprisesdiamond feedstock that has diamond particles that have a dimension inthe range of less than about 1 nanometer to more than about 100 microns.49. A joint as recited in claim 42 wherein said diamond load bearing andarticulation surfaces is a continuous diamond surface.
 50. A joint asrecited in claim 42 wherein said diamond load bearing and articulationsurface is a discontinuous diamond surface.
 51. A joint as recited inclaim 42 wherein said diamond load bearing and articulation surface is asegmented diamond surface.
 52. A joint as recited in claim 42 wherein alip is present on said substrate in order to interlock said diamondlayer to said substrate.
 53. A joint as recited in claim 42 furthercomprising CoCr solvent-catalyst metal in said diamond tableinterstitial spaces.
 54. A joint as recited in claim 42 furthercomprising a continuous gradient in said diamond layer.
 55. A joint asrecited in claim 42 further comprising an incremental gradient in saiddiamond layer.
 56. A joint as recited in claim 55 wherein saidincremental gradient includes a plurality of strata in said diamondlayer, a first of said strata having characteristics which differ fromthose of a second strata.
 57. A joint as recited in claim 56 whereinsaid differing characteristics of said strata are selected from thegroup consisting of diamond particle size, diamond particledistribution, and solvent-catalyst metal content.
 58. A joint as recitedin claim 42 further comprising an interface gradient.
 59. A joint asrecited in claim 42 wherein said diamond layer has a thickness of fromless than about 1 micron to more than about 3000 microns.
 60. A joint asrecited in claim 29 wherein said counter bearing material is not as hardas said polycrystalline diamond.